An upgrade from XP Home to XP Pro should be no more problem than installing a service pack. It should recognize all your drivers as XP and even migrate your registry settings, installed programs, and preferences. Always choose an upgrade rather than new install to save yourself a lot of headaches. I assume you've got at least 50% or 20 GB (whichever is more) free space on your disc.
Of course, something could go wrong. <g>
Always back up your data and know you have all your original install discs before your start anything like this. Also, write down anything you can find out about your computer including component manufacturers, models, and chipsets. DeviceManager (Classic Control Panel > System > Hardware) is a good place to start; but you may have to go further to find what you really need. Pay particular attention to anything having to do with display adapters and sound controllers. Those handy install discs from the manufacturer may have drivers for 20 or more video cards, possibly multiple motherboards, and may not have an auto-discover feature.
I'm a 30-year geek who's always killing my computer, so here's what I do. I use a utility like Norton GhostTM ($70) to create an image of my disc. These utilities make a bit-by-bit copy of the disc, regardless of what operating system is on it. It may require opening your computer case and physically removing your hard disc. It will require having a spare scratch disc you can use to copy your image to and possibly a third disc to install your upgraded system on.
I make an image of my disc as soon as I unpack the computer, before I turn it on the first time. This way I can always come back to a virgin, factory configured, environment. Once I have the computer running stably I get another image with all my programs installed. Then I pull another image before I make a major ugrade. And, another image in the new stable condition.
Of course, I never store any data on the C: drive. If it's not on a network drive or a second physical drive in my computer, I use a utility like Norton Partition MagicTM (another $70; Google "Partition Magic" for competitors) to split the original factory disc into 2 or more logical drives. Then I independently image the operating system (for restore) and the data (for backup).
Whew! Good luck if you follow through on all these suggestions.