How to change the remote repository for a git submodule?

You should just be able to edit the .gitmodules file to update the URL and then run git submodule sync --recursive to reflect that change to the superproject and your working copy.

Then you need to go to the .git/modules/path_to_submodule dir and change its config file to update git path.

If repo history is different then you need to checkout new branch manually:

git submodule sync --recursive
cd <submodule_dir> 

git fetch
git checkout origin/master
git branch master -f
git checkout master

With Git 2.25 (Q1 2020), you can modify it.
See "Git submodule URL changed" and the new command:

git submodule set-url -- <path> <newurl>

(On the -- separator, see "double hyphen as a signal to stop option interpretation and treat all following arguments literally")

WARNING: Hi-Angel mentions in the comments (tested even with Git 2.31.1):

One should be careful with git submodule set-url because it has a bug:

If, inside your .gitmodules file, the path looks like this some-path, and then you execute a:

# Usually causes unexpected behavior
git submodule set-url some-path/ new-url

(note the trailing slash / in some-path/), then, instead of modifying existing submodule, the command will add another one. Instead run:

# Good
git submodule set-url some-path new-url

That replaces the pre-Git 2.25 commands, which were:

git config -f .gitmodules submodule.<submodule_path>.url <new_url>
git config -f .git/config submodule.<submodule_path>.url <new_url>
git submodule sync
git submodule update --init --remote

Original answer (May 2009, fourteen years ago)

Actually, a patch has been submitted in April 2009 to clarify gitmodule role.

So now the .gitmodules documentation does not yet include:

The .gitmodules file, located in the top-level directory of a git working tree, is a text file with a syntax matching the requirements -of linkgit:git-config4.
[NEW]:
As this file is managed by Git, it tracks the +records of a project's submodules.
Information stored in this file is used as a hint to prime the authoritative version of the record stored in the project configuration file.
User specific record changes (e.g., to account for differences in submodule URLs due to networking situations) should be made to the configuration file, while record changes to be propagated (e.g., +due to a relocation of the submodule source) should be made to this file.

That pretty much confirm Jim's answer.

If you follow this git submodule tutorial, you see you need a "git submodule init" to add the submodule repository URLs to .git/config.

"git submodule sync" has been added in August 2008 precisely to make that task easier when URL changes (especially if the number of submodules is important).
The associate script with that command is straightforward enough:

module_list "$@" |
while read mode sha1 stage path
do
    name=$(module_name "$path")
    url=$(git config -f .gitmodules --get submodule."$name".url)
    if test -e "$path"/.git
    then
    (
        unset GIT_DIR
        cd "$path"
        remote=$(get_default_remote)
        say "Synchronizing submodule url for '$name'"
        git config remote."$remote".url "$url"
    )
    fi
done

The goal remains: git config remote."$remote".url "$url"

Note:

Git 2.40 (Q1 2023) clarifies git config remote.<remote>.url:

See commit d390e08 (07 Feb 2023) by Calvin Wan (CalvinWan0101).
^{(Merged by Junio C Hamano -- gitster -- in commit 59397e9, 15 Feb 2023)}

Documentation: clarify multiple pushurls vs urls

^{Signed-off-by: Calvin Wan}

In a remote with multiple configured URLs, git remote -v^(man) shows the correct url that fetch uses.

However, git config remote.<remote>.url^(man) returns the last defined url instead.

This discrepancy can cause confusion for users with a remote defined as such, since any url defined after the first essentially acts as a pushurl.

Add documentation to clarify how fetch interacts with multiple urls and how push interacts with multiple pushurls and urls.

urls-remotes now includes in its man page:

The <pushurl> is used for pushes only.

It is optional and defaults to <URL>.

Pushing to a remote affects all defined pushurls or to all defined urls if no pushurls are defined.
Fetch, however, will only fetch from the first defined url if muliple urls are defined.

Git 2.44 (Q1 2024), batch 10, tightens URL checks fsck makes in a URL recorded for submodules.

So when you change the URL, the URL validity check is now more robust.

See commit 8430b43, commit 7e2fc39, commit 6af2c4a, commit 13320ff (18 Jan 2024) by Victoria Dye (vdye).
^{(Merged by Junio C Hamano -- gitster -- in commit 76bd129, 26 Jan 2024)}

submodule-config.c: strengthen URL fsck check

^{Signed-off-by: Victoria Dye}

Update the validation of "curl URL" submodule URLs (i.e.
those that specify an "http[s]" or "ftp[s]" protocol) in 'check_submodule_url()' to catch more invalid URLs.
The existing validation using 'credential_from_url_gently()' parses certain URLs incorrectly, leading to invalid submodule URLs passing 'git fsck'^(man) checks.
Conversely, 'url_normalize()' - used to validate remote URLs in 'remote_get()' - correctly identifies the invalid URLs missed by 'credential_from_url_gently()'.

To catch more invalid cases, replace 'credential_from_url_gently()' with 'url_normalize()' followed by a 'url_decode()' and a check for newlines (mirroring 'check_url_component()' in the 'credential_from_url_gently()' validation).

These commands will do the work on command prompt without altering any files on local repository

git config --file=.gitmodules submodule.Submod.url https://github.com/username/ABC.git
git config --file=.gitmodules submodule.Submod.branch Development
git submodule sync
git submodule update --init --recursive --remote

Please look at the blog for screenshots: Changing GIT submodules URL/Branch to other URL/branch of same repository

In simple terms, you just need to edit the .gitmodules file, then resync and update:

Edit the file, either via a git command or directly:

git config --file=.gitmodules -e

or just:

vim .gitmodules

then resync and update:

git submodule sync
git submodule update --init --recursive --remote

What worked for me (on Windows, using git version 1.8.3.msysgit.0):

• Update .gitmodules with the URL to the new repository
• Remove the corresponding line from the ".git/config" file
• Delete the corresponding directory in the ".git/modules/external" directory (".git/modules" for recent git versions)
• Delete the checked out submodule directory itself (unsure if this is necessary)
• Run git submodule init and git submodule update
• Make sure the checked out submodule is at the correct commit, and commit that, since it's likely that the hash will be different

After doing all that, everything is in the state I would expect. I imagine other users of the repository will have similar pain when they come to update though - it would be wise to explain these steps in your commit message!

Just edit your .git/config file. For example; if you have a "common" submodule you can do this in the super-module:

git config submodule.common.url /data/my_local_common

git config --file=.gitmodules -e opens the default editor in which you can update the path