I don't have the app, but if deletion is possible here are the usual methods.
First; look for a Delete or Select button on the file list or thumbnail view of the jigsaws (which ever it has). Tap that, start tapping files to delete and a trashcan or delete button should appear.
Alternatively:
If you see thumbnails try long pressing on one to see if the screen changes to a selection screen (you can tap on items to select them) or a popup menu appears with the delete option. If selection is possible a delete button or trash icon should appear.
If you see listed items, try swiping on them, left or right, to see if you get a delete option; similar to how you can delete emails in Mail.
Good luck.