I think as long as they are younger than 32 and you keep making money, you can keep your guys. If you can't make money, you need to make changes indeed. Checking your roster, I think you already made some, but if you still have difficulty you might want to look to replace your players with more salary efficient ones. The center you're selling now is an example of a player that's expensive for what he's giving you; a player half his salary can give you the same production.
But if your other players are salary efficient and you make some good money, there's no need to sell your players. You could just invest the money you're earning into your arena.