If you need to rename your local git branch
$git branch -m<old-name><new-name>
this command is used for changing the name of branches while it is pointed to another branch.
If you need to change the name of a remote branch then
$git branch -m<new-name>
this will be handy to use when you need to rename your remote branch.
There is one more command
$git push origin <new-branch-name>: master
this command is used to pushing the changes to the master after your local branch is re-named.
Note: Changes will go to the master branch but the local branch name remains a modified name (ie:-new-branch-name).
For more commands like this please go through the following tutorial that will help you understand the git