Firstly, I want to commend you for trying to work on it. It is a middah that if not worked on will just grow and develop.
One idea might be to channel it properly. Be jealous of things that will make you grow. Kinas sofrim tarbeh chochma.
Another idea is to look at it as something that you cannot possibly attain because you are in a different position. I will explain. A twelfth grader can be jealous of chessed head, editor in chief, and valedictorian. She will not be jealous of the 5th grader who just got a main part in her class play. Because she understands that it is not a possibility for her. She thinks the chessed head was a possibility. But since she doesn’t think she can get a part in a fifth grade play. She’s not jealous.
think of it in terms of a car stuck in traffic. When you see a car in the next lane moving smoothly along, you get jealous because you think that you could be in the next lane. But you don’t get jealous of a bird flying overhead and getting there quicker – because you can’t fly. But you can’t be in the next lane either. It is not yours.
If you realize that something which is not yours is just as unattainable as flying or a part in the 5th grad play, then you cannot be jealous.