Undo last commit

Keep the changes, drop the commit

Removes the commit but leaves the changes staged in your working tree:

git reset --soft HEAD~1

Discard the commit and its changes

Destructive — the changes are gone from the working tree:

git reset --hard HEAD~1

Amend the last commit

Change the message, or stage more files and fold them in:

git commit --amend -m "New message"
# or stage more files, then:
git commit --amend --no-edit

After pushing

Reset and amend rewrite history, so you need to force-push. Always --force-with-lease over --force — it refuses to overwrite work pushed by someone else in the meantime:

git push --force-with-lease

Reset too hard?

git reflog keeps every commit HEAD has touched for ~90 days — see Recover from a bad reset.