Some installations of PSP leave behind a whopping chunk of installation files. These are left to assist in repairing the installation without having to reload the CD or the download file, should repair be necessary. If you keep the CD or the download file, you may safely delete the "Installation Files" folder.
After deleting this folder, it is a good idea to remove the installer-defined shortcut to PSP on your Desktop and replace it with one you create. Right-click on the shortcut and choose Delete from the context menu. Then browse to the Corel PSP program folder, find the PSP program .exe file (called Corel Paint Shop Pro Photo.exe), right-click on that file and choose Create Shortcut from the context menu. Then just move this shortcut to your Desktop.