Well, even if you go to a mechanic it's good to understand what the job is about. It's really bad to be halfway into a DIY job before discovering you're in over your head.

Since you're 'supposed' to get fresh anti-freeze every couple years, you probably don't know what's in there. Mixing different types of anti-corrosion packages isn't good. Honda coolant is good but if 3-year-old bright-green Prestone is in there now, you probably don't want to mix. That's why you should rinse it several times to get rid of all the old stuff.