When you run the installer for 1.03, it will ask you if you want to uninstall the previous version.
Click yes, and it will automatically uninstall 1.02 and then install the new version 1.03.
Just have run acros this, have version 1.02, I did download 1.03, do I uninstall 1.02, seems like I did that from build 6 to 1.02, but cant remember for sure. BYW I have XP HE SP2 if that makes any difference. TIA Ronnie