If it is the last commit you do you can do it with:
git reset --hard HEAD~
If it is one of the last commits in the same branch you can do it with:
git reset --hard HEAD~2
And so on depending on what commit you want to delete.
You must to delete first locally and then execute:
git push origin +BRANCH_YOU_WANT_TO_RESTORE_THE_COMMIT
Sources: adrian.ancona's website and stackoverflow