Needed PHP Files – Help With Fixing Infected PHP Files

Hello. My sites got infected with a php virus and I’ve been working hard to take the codes out. Does anyone know if I could just replace some files and what files I need to have, in order to keep everything on my sites?

I am going to move to a new server and believe I could keep the updates, from the database. But the files I would have to keep, in order to keep everything on the site. I have never done this, so please understand.