I'm thinking of painting the rear window trim does anyone know how to remove it?

 

a reaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa aaaaaaaly big crowbar!!!!!!!!

 

remove rear inside trim panel pieces

then remove back window - unbolts but the butyl is set hard which makes the window a bit of a pain to get out

then once the back window is out you can unbolt the trim piece, also take out the 3rd brake lamp

 

You might want to shop for a used rear window assembly (or just the trim, but most places probably will not separate).
A friend of mine bought one to replace a broken window, and I don't think he paid more than $100.
That way you can take your time and experiment on one that is a spare, also good in case you do not like it.

By the way, older F-150s (I think my friend's was a 99) had flat plastic trim around the window, not textured like the ones on the trucks today. I would look for that one as it would be better looking painted than the textured one.