Is it safe to use disc cleanup to remove 'old' folders from system

I have upgraded my Windows 7 Home Premium to Professional and as part of the process I was told that files would be saved to old. Can these be cleaned from the system or do they contain vital information for the current OS?
My computer is a Dell XPS Studio 8000.
I want to create an image of my computer to removable media and at the moment my OS is 830GB. I am assuming that the old files are taking up quite alot of this.
I would create a restore point before doing this but don't want to do something I shouldn't.

Yes you can delete the "Old Folder".

You MAY experience problems though since you did an "upgrade" install instead of a clean or custom install. Nearly everyone who has done the upgrade install have experienced problems, maybe not right away but within a few days or so.

You CAN do a clean install if you have the "Upgrade" discs too. It has been done by many users.