Jesus Christ! 90% of the answers here are absolute nonsense. Guys, no offense, but if you have no clue what the user is asking, just don't reply. And learn better english as well...
The guy started the thread by asking a VERY SIMPLE QUESTION for crying out loud. He is wondering about the Upgrade Version as opposed to the Full Version.
The Clean installation is another thing and the user made it a 100 times clear that he is aware about it and that he wants to know has to do with the Upgrade version and whether it's the right one for him...
...and yet...3 pages of absolute stupid answers...
Anyway, my friend the answer is Yes, you should buy the Upgrade Version and Yes, with that version you can "convert" your 32 XP to 64 Windows 7.