Forcefully Change History
Assuming you don't just want to delete the last commit, but you want to delete specific commits of the last n commits, go with:
git rebase -i HEAD~<number of commits to go back>, so git rebase -i HEAD~5 if you want to see the last five commits.
Then in the text editor change the word pick to drop next to every commit you would like to remove. Save and quit the editor. Voila!
Additively Change History
Try git revert <commit hash>. Revert will create a new commit that undoes the specified commit.
