Why do you need to cover your tracks? You're obviously allowed to use the internet, or else you wouldn't be able to post here, so what's the big deal?

At any rate, it's doubtful your parents will go looking for the file, so you probably just have to get rid of the obvious tracks, namely your browser history. If you want specifics on how to delete the entries you want gone, you'll need to post which browser (program to access the internet pages) you're using. If you want to be super careful, you can also delete the cookies related to the websites.