Need help with my car stereo

Oh ive given msot of the wires theyre fair share of wiggling.
I wanted to just add a sub but i suppose i should fix the rest before anything else.

Any ideas on how to find out for 100% sure if thats a sub without ripping the entire car apart.
I couldnt see any civilized way to remove the back deck.

also, suggestions on specific equipment for an upgrade would be nice since im novice with car audio