Disconnect a very small connector on each side. (These are for the sounder).

Remove a long screw on each side.

Remove a short screw on each side. (Ensure that it is indeed the short screw that you use here on reassembly.)

The two circuit boards at right angles should now lift off.

There is also a sounder on each side which must be prised off and refitted to the new central frame. Again, take care to correctly route the cable.