File > Preferences> Reset Preferences.

Check only the One on the bottom:
Delete all cache files. Active caches rebuilt on restart. Click OK.

The next time you start PSP, it will take more time to open. When you open Picture Tubes, or Masks, or Preset Shapes or Brushes, it will run again, delaying the start of these features. Be patient because it only does it once. When PSP gives you a list of duplicated items in that folder, highlight the list to copy it to your clipboard. (Click on the top item, press your Shift key and click on the bottom item to select all of the list BEFORE you click Copy to Clipboard.) Open Notepad and click paste. Save the txt file so you can use it to clean out one of each of the duplicate items. You can also rename them. Your call.

If you really want to do the job right, check your Tubes, Masks, Shapes and Brushes in the first opening of PSP, save individual lists of duplicates and clean the folders all at the same 'sitting'. Close PSP before you work inside the folders. Open PSP again. Repeat the Delete all cache files setting. Sometimes PSP finds more duplicates on the second go-round.

Uncheck the Delete All Cache Settings when the job is done.

Monthly maintenance keeps PSP running fast and clean.