What can I do to repair the hydraulic trim for my 90 hp Yahama outboard engine? Engine in up position.?

I can hear the motor when the switch is pressed but the shaft for the hydraulic lift does not move. The engine worked nicely about 7 days ago and the seals for the 3 hydraulic pistons were renewed May, 2008 a $480.00 job. I am taking the engine back to the shop but I'd like to learn how to do it myself.