Remove Insert from Plastic Keyring

I wanted to put new inserts in some plastic keyrings I have. The difficulty I have is in removing the plastic cover to put in the new insert. If I bang them off a hard surface enough times I can get it removed but have quite a few to do so looking for easier way. Wondering if anybody might have any ideas??? Thks a mil

I got some very nice ones from Ebay. Photograph one one side and instructions for set of keys on other. Got 20 for about €20. Good luck Browtal