There are several bronze colored screws (red) holding the black plastic frame to the circuit board and backplane.

No need to remove the heatsink at this time, although the IC output amplifiers are soldered to the PCB and will hold the heatsink in place.

The hot glue needs to be removed as well.

Try prying the backplane loose first

When the backplane is removed, the circuit board comes off by moving it up over the plastic posts.