If your van has the speakers in the side panels above the wheel wells, they are 6x9.
To remove them, you have to undo the screws along the side barn door on the pannel up to about the window glass. Nest, remove the screws along the metal trim piece from below the windows all the way back. This allows the plastic panel to be popped outward for easy of access. The plastic grill covers are press fitted in. Good metal speaker grills should work better. BOSS is one brand I went with for the rear to maintain the bass. The front doors each have 6x9 and the dash has 4x4 I believe. Replaced all of them back in the Spring.
When replacing, get speakers with the plastic cones. The felt is junk and rots, cracks and distorts the sound over time. The money is well worth it.