Use a flat pry tool (such as a flat-blade screwdriver) to prop up an edge of the subwoofer.

In my case, I just used the Phillips #2 screwdriver I had on-hand.

Slide your fingers underneath the sub so that you get a good grip on its edge.

Carefully lift the subwoofer out of the enclosure, minding any wires that may be tethering the sub to the enclosure.