I have the Peachtree Decco and if the construction is the same the way you do it is to take out the screws that hold the feet to the case. That will free the outer case from the interior metal case and allow you to slide the interior out from the rear by pushing on the front.
On my Decco a thin line of the exterior finish around the rear edges was acting as a glue to hold the two together even after the screws were removed but I was able to work it free.
On my Decco a thin line of the exterior finish around the rear edges was acting as a glue to hold the two together even after the screws were removed but I was able to work it free.