I have a problem with relaxing my shoulders also. Really, it's my right shoulder. I noticed it whilst preparing for a recital one day; that it was stiff, and I was holding it up. So when practicing, at times, I will make sure BOTH shoulders hang like a hanger, my back is straight, my arms are relaxed, and my elbows aren't sticking out. If I feel I'm rather tense, I jiggle my shoulders, arms, and wrists, and focus on relaxing ALL my muscles. This often helps!
But since you said your shoulders are raised, Make sure you let them hang like a hanger, and that your elbows are by your side, NOT sticking out!!!
This is what I focus on when I feel tension, and that my shoulders are raised, and it helps! It's a very large part of my technique. I hope it helps you as it has helped me!