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>