It would be a good idea to keep your PAF4 ".paf" files. Depending on where you have them, you should be able to delete PAF4 and retain them. Just make sure they are not in the same dirctory as your PAF4 program. Move them to your desktop or another safe place if need be.
Depending on how you installed your PAF4 originally, you can un-install it (correctly) by going through START|SETTINGS|CONTROL PANEL|ADD/REMOVE PROGRAMS, highlight PAF4 (make sure it IS 4 and not 5!) and then click remove.
If it is not in the listing of programs in ADD/REMOVE Programs, you will then have to uninstall it by deleting the program folder.
However, don't be in a rush to uninstall PAF4, as you have only installed PAF5 today. If you can spare the space, leave it there for a while just in case you have to come back to it for some reason. You can always delete it when you are entirely satisfied with PAF5 (and you should be).