After you call them and they confirm through scripted troubleshooting that it does indeed need replacing, they will send you a new box via FedEx, UPS, or DHL. Sometime they have you pay the shipping, sometimes not. Shipping is about $20, but I don't think this is charged if you have the Protection Plan.
After the new box arrives, you do the swap yourself, and take the old HR20 and put it in the same shipping box as the new one arrived in, and affix the RMA tag to the outside of the box, and drop it off at your nearest shipping office for that carrier, or call that carrier for home pick-up.