were do i drain & refill my gearbox on my 2003 d5 as i need to do it my self

There is a drain plug that os accessed under the transmission and it is 22mm (wrench size) and it is vertical in it's position. It takes Volvo Synthetic fluid. if you put any other fluid that is not compatible, you will damage the transmission and will require replacement. You will only be able to drain 2.5 to 3 quarts from the drain plug. The transmission should be flushed.