RE: How to split up routine?
Yes you should rearrange it. If you're going to train a bodypart on its own on one day, it stands to reason it should be a reasonably big one. Shoulders are not very big and don't require a lot of work to grow, especially since they are worked in most chest and triceps movements as well.
Personally I'd just put shoulders with chest and triceps (just do plenty of overhead pressing) and cut down to three days. If you must train 4 times a week, Chest/Back/Shoulders+Arms/Legs would be better than what you have already. Personally I don't think muscle groups are easily split up into four sensible sections. That is assuming each is trained once a week. If you do some more than once a week, 4 days could be very effective.