the dishes are coming clean on bottom shelf but dont come clean on top
Often this is dirty filters etc. in the machine.
May also be the unit is not getting enough water but usually the pump will sound different due to it sucking air.
Most units fill to just under the heating element.
This is easy to check, just add a couple quarts of hot water after a fill if the upper arms now operate correctly then that is your problem.
Be careful to not overfill it.