Windows 7 Home to Windows 7 Pro

Should be able to via the Anytime Upgrade... however if you're going from 32-bit to 64-bit (or vice versa), a clean install will be required. No partitioning required in either case.

even if you do a clean install, your partitions should stay the same. you would only have to format the side with windows installed on it (if you do a clean install). if you have any Programs installed on your other partition, you might run into some problems launching them once you put on PRO. So to sum it up, Your DATA storage partition can be left untouched, and you can do a clean install on your WINDOWS boot partition side.
word of caution: if you can, back up your files just in case.

Windows Anytime Upgrade is the best option for you.