If you sealed the decals with Mod Podge to the proper thickness (I hope you did!), removing it is a snap! Use your fingernail and start at the edge of the Mod Podge, and work it until you can start to pull on the Mod Podge, and then it will remove in nice big sheets. It is even easier than removing the decals themselves!
Our decals are easy to apply, and easy to remove. Cheap stickers are weak and will tear and shred rather than just come off. Our decals are strong. Use your finger nail to get under an edge of the decal, and work it free till you can grasp it.
Then pull up and back slowly, working it back and forth, and the decal will come free. The decal may leave some adhesive you can feel with a finger, but a little rubbing alcohol will remove that.