Save your work first just in case, then uninstall the old, install the new for the best results. In theory uninstalling Office does not delete documents but there have been reports of loss.
Given what's at stake why not have a backup copy?
I have an illegal copy of Microsoft Office Pro 2003 on my Windows XP desktop. I just purchased a legit copy of the program. Do I uninstall the old one and reinstall the new one? Could I potentially lose any documents if they are not backed up? Last question, can I just enter the new Product Key? Thank you to anyone with an answer.