Undo changes to tracked files with:

git reset HEAD --hard

Remove untracked files with:

git clean -f

Remove untracked files and directories with:

git clean -fd

but you can't undo change to untracked files.

Remove ignored and untracked files and directories:

git clean -fdx

git push -d <remote_name> <branch_name>

Note that in most cases the remote name is origin.

git branch -d <branch_name>

git branch -D <branch_name>

If you want to rename a branch while pointed to any branch, do:

git branch -m <oldname> <newname>

If you want to rename the current branch, you can do:

git branch -m <newname>

A way to remember this, is -m is for "move" (or mv), which is how you rename files.

git checkout <branch_name>
git pull origin <branch_name>
git merge <with_branch_name>
git push origin <branch_name>

You can simply commit again, using the --amend flag:

git commit --amend -m ""

git reset --hard <commit-hash>
git push -f origin <branch_name>