You can scream sing if you practice and learn on how to regulate your own breathing in a way that lets out little air at a time. You need to use your diaphragm to control the pitch. Sing along to music done by your favorite bands but do it as if you are screaming, paying keen attention to your voice so that you rectify where necessary.
honestly it's not that hard. it's basically screaming words. try turning your favorite song up a lot (when your home alone of coarse, you dont want to piss off your parents or sibling. lol) and just scream along with the song. i do this a lot and it's super fun. :D