I installed the new blower yesterday. Its not difficult technically, but it is difficult physically. I'm relatively fit (185 lbs, 6'2"), but its pretty difficult to get under there and get your arms in the right positions. Amazingly its even harder than working under the dash of my tiny 72 MG Midget, the same "sit backwards on the seat then lay on your back with your legs in there air" trick doesn't work as well in the Volt. You'll also need a 7mm and 5.5mm ratchet socket, which is I think the only time I've ever used my 5.5mm socket.
The bottom trim panel is held in by three screws, one visible in the front, one on the front right that's partially hidden by the right rocker panel trim, and one in the back that's recessed and hard to see. You don't need to remove the right rocker trim to remove the screw, you can push the corner in enough to get to the screw. Once you have that off, there's one more screw in the floor air duct, and once that's out you have to wrestle with the duct a bit to remove it, but it'll pop out. You don't have to remove it completely to get the blower motor out, but personally I couldn't reach the blower plug without removing the duct. Installation is the reverse. Probably took 30 minutes, and I could probably do it in 10 minutes if I had to do it again.
The new blower definitely works better than the old one, more air and less noise. I am occasionally still having an issue where the fan runs full speed, but I'm not always getting as much air as I should. I think there might be an issue where the doors that control the flow of air might not be opening and closing entirely.