Apple trade-in process for a new Mac purchase

Yes, you can start the process online at the following website.

click here ➜ Apple Trade In - Apple

Not sure if they are taking in iMacs in store, but you can always inquire. But yes, they will take in an older Mac and give you credit for it.

You can also start the trade-in process during an online purchase in the Apple Online Store by clicking the "Get Started" link under Trade-In. Enter your Mac's serial number and other details and it will provide a tentative trade in value for it, pending final review by Apple or their trade-in partner.

If you ship your old Mac it to Apple in the container that they provide with the new Mac (or shortly thereafter) be sure to take photos at different stages of the packing in case the shipper damages the item during shipping. It's happened before here and the user didn't have photos so it was he said - he said.

If you ask and they say you can take it in to the Apple store that would be the best solution. However I believe that would be OK only if you bought a model from the store and not online. Check that when you call them. If purchased online they will send a shipping container to ship the old Mac back to Apple.