Revert Windows on MacBook?

I have a MacBook. It runs both Mac OS: X and Windows. Accidentally, I installed a virus on the the Windows side. Mac was unaffected, while Windows became slower than ever. I ran several antivirus programs, 2 of which picked up nothing, the other founded viruses, but couldn’t delete them. I heard that one could some how revert the Windows side (when I didn’t have the virus) to origonally how it came on the disc. Does anyone know how to do this and/or if this is a good plan? Thanks. I have certainly learned my lesson on not downloading files on Windows!