The heater case does need to come out to replace the blower motor. The bolt holding the dash to the cowl on the passenger side and the brace below the glove box need to be removed so the lower right portion of the dash can be pulled out. The dash pad needs to be removed as well. All this is detailed in the factory shop manual.
While you have the blower case out, it is probably a good idea to replace the heater core and the foam seals on the case and air-control flaps and doors.