If you want to upgrade, you will most likely require the XP discs (plus SP2 later). Microsoft doesn't supply the formers as freeware.
Just make sure your system is capable of being upgraded to what you require. If you are upgrading from 98, you might find your memory gets curtailed. Depends on your system.
My peers on this site will advise you better. Like you, I am a novice, too.
Whatever upgrade decsions you make, I suggest the usual: back-up everything you have/want/need/etc before you try and upgrade. This is simply in order to avoid disappointment later.
Good luck, and please tell this foirum how you get on.