How should I tell my roommates I want to move out?

I live with 2roommates in a very small apt in NYC. They’re fine and all but when the lease is up in august, I want to move to Brooklyn and live alone. Problem is, they assumed we’d all live together for the duration if college. I need to tell them soon, but I don’t know when or how to bring it up or what to say. Its very important as they’re both my good and only friends.