git reset HEAD~
This leaves your working tree (the state of your files on disk) unchanged but undoes the commit and leaves the changes you committed unstaged (so they'll appear as "Changes not staged for commit" in git status, and you'll need to add them again before committing). If you only want to add more changes to the previous commit, or change the commit message1, you could use git reset --soft HEAD~
instead, which is like git reset HEAD~
but leaves your existing changes staged.