How do you change power trim fluid 1999 225hp Yamaha

[tinnerman]

I have a 99 225 EFI Yamaha... (just purchased)
power trim Fluid ia very dirty and smells burnt.
It sounds like air in system when operating but works fine otherwiseIf apears to be full at the vent hole .
Thought I would change the fluid
How do you do that ???
the online manual says use Drexon II::