Jesus can free you. Confess your sins to him and believe that he died on the cross to save you from eternal hellfire.
Since you've already been possessed, you need to take it seriously; you'll need to find a (real) church nearby and attend so the demon stays away, they do come back.
You will also need to get baptized (full immersion in water) by another Christian, a good southern baptist or nondenominational church can do this. they should have a sunday livestream you can check to make sure you're not walking into a church that is comped. This is the type of church you should look for; they can even help find one near you.