Use git command line (with git bash on Windows) to change the branch name.

1 – Be sure you are on the right branch

Firstly, you should be on your current branch (the branch you want to rename) with git checkout.

2 – Change the name of the branch locally

Secondly, you should rename the branch with the following command:

git branch -m <the_new_branch_name>

The new branch name should be valid, with no space. If you use special characters you should use quotes like:

git branch -m “let’s-put-a-complicated-name”

3 – Change the name of the branch remotely

You can now change the name of the branch remotely so it’s also changed on github / gitlab / bitbucket etc.
To do push it use:

git push origin HEAD:<old_branch_name>

If it’s a complicated name you can still use the quotes:
git push origin HEAD:”it’s-an-old-branch-name”