How much trouble is it to convert air shocks to regular coil shocks?

i have a 2000 expedition(eddie bauer) and i noticed that the rear of the truck has already been converted to coil shocks but they left the front and i suspect there no good,the air compressor comes on but i never see or notice a difference but my main concern is the truck is tilted pretty bad to the right ,it is a good couple inches lower than the left side(unleveled) and if the air shock is out on right side ,how much trouble is it to swap out the air shock for the coil spring shock(and does it have to be a heavy duty) weight is about 7200lbs. with full capacity