Assuming its a coversion van you need a thin open ended wrench about 1 3/4". looking just below the sliders you will see a large bearing plat that lets the seats turn. On top there is a center nut that is hard to reach and has the nylon locking material to prevent it from backing off. Untighten (counter clockwize) until you have removed the nut then lift the seat off. The base is usually welded to the floor bu the conversion company so you need a grinder if you going all out.
YOU WILL HAVE TO REMOVE THE REAR SEATS. THE SPEAKER GRILLS AND THE PANEL IN THE WINDOW IS ONE PIECE.
Remove seats
Just heater outlets for the rear area. If you were to remove the console assembly which hides the engine cover, you would see a duct running from the top to beneath the floor. It feeds the vents you mentioned.
the rear speakers can be removed by getting a 5/16 inch socket and loosen the bolts holding them in
fold seat down, then unbolt the frame of the seat, and remove them. it is a really simple process.
get into the passenger part of the car and then remove the rear seats or call the AA
Chainsaw
in the boot, remove the carpet and it should be in the right hand corner towards the rear seats
There should be a strap at the rear bottom base of the seats. Pull this strap and tip forward. The seats will lift out.
it is under rear seats
1996-2007
remove both harnesses then remove 2 front mounting bolts and 1 rear pull on belt in order to loosen tentioner and remove installation is oppposite of removal