1999 subwoofer

Hi all, I'm new to this forum so treat me well if this has been covered somewhere else.

I have a a '99 Frontier SE 6 4x4 and the stock subwoofer on the back wall of the cabin is blown. I got a replacement for free and am ready to put it in, but I can't figure out how the darn thing comes off. Anyone know? Your help is greatly appreciated.

Also, any good alternatives to the stock sub?

I am running on the '00 XE, it doesn't have Subs in the back... so I bought two Alpine Type E, which is Entry class, 500 watt each, and an Alpine 700 Watt Mono amp, all for about... a hundred something bucks...
Add box and wiring... total 200!
SOunds GREAT