tilt and trim

tilt and trim is making a clicking noise on the way down .a friend says it has air in it to bleed the trim. if so how i do that. the motor is a 2002 yamaha 115 four stroke.

[boats.net]

The trim rams will making a popping noise when they come in contact with strike plates on steering bracket. Put grease on ends of trim rams to stop the popping noise.
To bleed trim system trim, trim up fully and fill with oil. Loosen manual release screw and allow motor to trim down under it's own weight. Retighten manual release screw and trim up, recheck trim fluid.