Question on wipieing system.

Hello, i just have a quick question here so hopefully someone could help. I have Windows 7 currently installed and i have the upgrade Cd next to me labeled " Windows 7 Home Premium (upgrade designed for windows vista )" So i upgraded a while back ago from vista, so my question is if i reinstall the cd will it give me a brand new system, wiped tottaly clean, free from any problems that i do now? Only reason why im asking is a family member of mine got a really bad virus and i cant fix the computer so i plan on wiping it, it could be good to becuase there is a lot of stuff on here i don't use. So will it wipe it totally clean? Thanks in advance