It should ask you right away. But if you got that far, it wont upgrade, you will either re-write the partition and format and then install xp pro. When you are on your desktop, you install the cd, it should say Install Windows XP, etc, etc, then do you want to upgrade or new installation (advanced), you would pick upgrade but it didnt give you that option so I guess you cant go about it that way, looks like you will have to reinstall everything. Do you have 2 hdds? If so, transfer your documents, etc to that hdd and install pro and you will be good to go.