Remove certain files from staging area
git reset HEAD -- <path/to/file>
Remove all files from staging area
git reset HEAD -- .
Rename current local branch
git branch -m <local-new-name>
Rename other local branch
git branch -m <local-old-name> <local-new-name>
Delete old remote branch, push new branch
git push origin :<remote-old-name> <local-new-name>
Set local branch to track new remote, upstream branch
git push -u origin <local-new-name>