I got backups so how i install them?

Hey, i got a question my blog just got hacked, i have backups files though. So how do i put back all those back up files back?? I mean all the files are on the server, its just one of the files got altered by hackers and dont know where and how to fix it, so i all start all over again by installing the back up files before the site got hacked.

So how do i start with these?