You don't need to uninstall the old version to install Windows XP SP3

Open the Registry
editor, find HKEY_LOCAL_MacHINE\\SYSTEM\\CurrentControlSet\\Control\\Windows, and find the DWord value CSDVerision in the right column.

If this value is:

hexadecimal 100, 256 decimal, the service pack version displayed by the system is SP1;

hexadecimal 200, Decimal 512, the service pack version displayed by the system is SP2;

300 in hexadecimal, 768 in decimal, the service pack version displayed by the system is SP3;

and so on. We will modify it to SP2, which is to modify it to hexadecimal 200, decimal 512. Deceive the program, you can directly install a new version of SP3.