Yes, do you know how? if not, backup using Time Machine, backup important files (I backed up most of my files) on an external drive as well just to be safe!
Insert the disk, boot up from the disk, use Disk Utility to erase your partition that Snow Leopard is on, you might need to format it again to be used for OSX, I think it is NFS+ Journelled or something.
Then continue with the installation. Don't migrate from an existing drive, or from Time Machine - otherwise it defeats the purpose.
Then drop the files you want back from external drive, and restore particular files you want from TM.
Be careful though!
I think I got that about right?