Vista > Windows 7 help!?

I have just purchased the 32-bit Professional Windows 7 Upgrade, and I need to know (in simple terms, lol) whether or not upgrading my OS will delete all my files?? I am illiterate with computers so any technical jargon will go over my head! I know you will talk about backing up files etc. which I will do, but I still want to know if it will delete the files just incase I can't get hold of a backup drive. Thanks in advance. Claire (UK)