Suse pro and pro upgrade

Hi The suse Website lists the Suse pro 7.3 as around 59 and the upgrade at around 35 (I think), both have 7cd's / 1 dvd and 5 manuals, 1. Is the upgrade only available to people with an older version of the professional set 2. Can I upgrade from say the personal ed 3. How does it detect I have a previous version, esp as I would eventually do a clean install and have probably sold the older version on. or given it away so someone else can benefit. Thanks for any help, I am currently using Red Hat, and have heard about problems with 7.2 mainly with the ext3 filesystem support and older kernels which don't support it very well. So I have decided to get Suse as my next upgrade. Paul