> Ride height is the term used for racing..but  a van is hardly a race vehicle..
shhh!!!! my van might hear you. :P

-- In any case, there is no adjustability in terms of ride height
built into the suspension. Your best bet is to make sure that, as
David has mentioned, the shocks are not unevenly worn, and also that
the springs have not gone out of spec.

If you are trying to corner-balance your van, you could always buy a
set of coil-overs for it. (I'm not sure offhand who makes them, but
Google always has answers.)

Good luck in any case,
Sudhir