remove second operating system

I installed a another version of windows xp, and then i realized the old version is still on the computer. I had thought when i install the new version it would just replace the old. So now i have two xp versions on my computer, and i want to delete the new version since its not genuine and its in Portuguese. I ws told i would have to reformat the drive to fix the problem. Is that correct? I do not want to loose the few files i have on there, but i did not wanted to having to copy everything. Any suggestions?