The motor is clamped inside a steel collar, that is attached to a steel vertical partition. There is only a single machine screw that clamps the collar together, over the motor. The motor has a shaft coming out of each end, in which two fan cages are attached. There are two wires connected to the motor, where it enters the collar. These are the 12v power supply and a ground wire at the collar. Look for these wires and you will see the collar screw.
To begin, make a rough sketch of the wiring, and disconnect the power.
To get the motor out, you need to lift up the black plastic shroud, which has the majority of the wiring attached to it. Most of the wires can remain connected at this point. First remove the printed circuit board assembly to make some room to work. This is on the left side, attached with a wing nut and it will slide out towards you with a bit of jiggling. There are four self tapping screws holding the shroud in place; after removing them gently lift the shroud towards you and upwards. You may have to disconnect a few spade connectors to make this possible. Be careful, the rather delicate sail switch is attached to the back of the shroud. You can use a piece of string to hold the shroud out of the way.
You will need to loosen the small fan cage, on the gas valve side of the vertical partition, to pull the motor out. Use a long allen wrench to loosen the grub screw, attaching it to the shaft. If you encounter any rust on the shaft, preventing the fan cage from sliding off, use a small file to remove the rust and a bit of oil. Rotate the fan on the shaft and you should be able to work it loose.
You may find it easier to remove the burner assembly and exhaust pipe to make more working room, but it is not necessary. If you want to do this, the exhaust pipe pulls straight out towards you, after you loosen a wing nut, but you will probably have to jiggle it, if has been in there long. The burner assembly is another matter, there are three self tapping screws and you will have to disconnect the propane fitting. It can be done but takes time and more jiggling.
Put it all back together, in the reverse order, with the new motor.
And you will be all set.