Any way to delete some of the puzzles I have complete?

Open the Jigsawscapes puzzle and go to My Puzzles and at the top of the page you should see the headings as - IN PROGRESS - FINISHED - COLLECTIONS. Then go to the puzzles you have finished and they should all have ticks on them.

Then hold down the ones you want to delete and you should be able to delete them on the next page. It's worked every time for me without a problem.