So, I wanted to fix my Scorn's eyes on his dino head. One of them is misplaced from right side. After removing the screw from the dino head it doesn't want to deattach. Is there something that I'm missing or it just hard to pull off on the first time?

 

It will detach with some pulling, the trouble is that there is the rubber teeth/crest piece which does not want to let go. Besides popping off the lower jaw, that ought to be the the only problem. Do be aware though that the eyes are painted onto the aforementioned piece.
Excuse the blurry photos, I was going single-handed to provide light
Notice, if you will, the pegs hidden within the snout which more or less anchor the head together. With a little persistence, they will release. From there, the rubber will want to stick to the nostril peg. Simply finagle it enough and you are all set. In short, yes, it is hard initially. Have a great day and may all go well.