Getting ready to change the coolant.....

in my newly acquired 99 Outback (66k miles). I have never changed the coolant myself on a Subaru before (I don't want to f it up). The question is, should I do this myself or take it to the dealer and have them do it? I have read about making sure you get all of the air out and stuff, but not sure if I know how. Also, what do you flush the system with? I read the manual and it sounds pretty easy, but it doesn't say anything about getting the trapped air out, so I'm kind of lost. Thanks for the help!