It should all remove easily *from the front*, without having to disassemble the dash or anything.

The sled is designed to be held in place by bendable metal tabs, just in from the front edge. Look closely at it, and you should notice many such tabs, but only 2-4 of them actually bent to hold it.

Just reach into the tab holes with bentnose pliers (or straight needlenose, or stiff wire, or a fork, or..) and put the bent tabs back up so that they are once again flush with the sled.

One they're all straight again, the sled should pull gently straight out from the dash. The cabling and tuner are probably stuffed in behind it.

There's a small chance that you may have to crawl in on your back and detach a small metal strap/screw from the centre/rear of the sled before it will budge. Some installers connect that, and some don't.

Cheers