Heat with a hairdryer - slowly and from a distance or it could blister the decal. Put the frame somewhere warm to start with to raise it's ambient temperature. Dependent on the decal could try some dental floss underneath if you can get a purchase by lifting a section.
I’m not sure heat will do much to the clear coat if they’re lacquered in. Possibly some thinners applied sparingly to try and remove it but it could damage the decal underneath.