You need to pull the fan out of the housing. As I remember it has three funny looking clips that hold it in place. Take pictures of the clips, and how they are used to aid reassembly.

And the blower squirrel cage has to come off. Soak it in penetrating oil. It can be a real bugger to get off. There is a little allen screw holding it in place. Remove the allen screw completely. The fan should slide off, but I had to cuss and fight with mine to get it off. Then reassembly.

Thanks, Glen. Not sure I've understood you correctly, but but the old fan is already out of the housing; you may have missed that post. The replacement comes as a unit with the cage. I had trouble attaching the spade connectors without disconnecting the harness. I think I'm going to need to pull it out a bit to have enough slack to install the new fan; just didn't want to end up damaging anything.

Problem solved. there's a small clip attaching the harness to the top that I didn't notice last night, which is why it wouldn't budge. This is what happens when you're impatient and work in a dark condo garage with a headlamp. Sorry about the confusion, guys.