I made my commits and pushed to github. Then, I realized that one is a wrong file and I forgot to add a new file. I would like to either completely undo or delete my pushed commit or add and delete the files from my pushed commits. Which is easier and what should I do?(I am the only one working on this repo so no one hasn't pulled or changed my commits.)
You can do this in a number of ways.
The first is the way "Lajos" mentioned - squash the commits into one. This has an impact on the version history, and rewriting public version histories is (as everyone else has pointed out) a bad thing. It can cause all kinds of nasty, and even if you're the only one that touches the repo it's still a good idea to get into the habit of not rewriting public version histories.
The better way is to do a reversion (git revert). This creates new commits that reverse the changes of the undesirable commit and does so by adding a new commit to the history rather than attempting to modify the existing public history.
See git-revert for more information.