Tilt and trim issues

[eli sanders]

1983 50 HP Mercury SN-642-1301. Before winter tilt and trim worked fine. I tried tilting up to haul and motor runs but no movement. I'm assuming just low fluid. If so where do I refill and how much. Thanks ahead for all help.

 

[haventaclue]

http://www.crowleymarine.com/mercury-outboard/parts/275_230.cfm This one? Open vent 5 and fill through 4 to level with threads.