What do I need to do to get ex out of my house?

If your divorce decree or settlment addresses the issue of where she can live, who is allowed to reside in the house, etc., follow the terms of said decree or settlement.
If the divorce decree does not address this issue and the divorce is final, you can remove her: anyone not an owner or rent-paying tenant may be removed from property at the owner's will except for a spouse, who cannot be removed from the marital home without a court order (e.g. decree) or a settlement in a court case requiring one spouse to go. But if your divorce is final, she is no longer your spouse; and if she is not your spouse, not an owner of the property, and not a rent paying tenant, she can remain only so long as you let her--and you can require her to leave at any time.
If she won't go when you ask her, you need to bring a kind of legal action traditionally called an action "for ejectment" (your state may have a different name for it). Think of this legal action as "eviction for guests" (anyone not an owner, not a tenant, and who was not a trespasser is a "guest"). The action requires that you send her the proper written notice(s) first to leave; then you have to file the action in in court in the correct way, providing proper notice of it to her. It is a "technical" action in that a small paperwork, etc. mistake can force you start over; you are therefore advised to retain a lawyer to help you. A landlord-tenant attorney should know how to do this and would be a good choice.