And just to flesh that out a little bit, you can transfer weeks with RCI using a form and a fee, if that is the deal you've made with your purchaser.
There is a way to transfer weeks with II as well, although previous threads about that have indicated that it's not the exact week that is transferred but a replacement sort of week, that would go into the purchaser's account, which may not have exactly the same trading power as the week being given up. It may be a bit better or a bit worse, as it's some sort of average of the weeks of that particular resort. There is a fee through II as well.