i just bought a honda civic and it has 90k miles on the engine and the automatic
transmission fluid looks like oil
I Need help changing my auto transmission fluid

 

honestly, your best bet is to go to a shop and pay whatever they charge for a trans fluid exchange.......you can watch the lines and see the old nasty fluid coming out, and the new clean fluid going in. if you dont want to do that then what you need to do is 1)open the drain plug(or loosen the pan if there is no plug) and drain all the fluid out(there is alot more fluid in the transmission that will not drain out so if the manual says your trans takes 5 quarts......5 quarts wont drain out of it), 2)put the plug back in or tighten the pan up, 3)fill the tranny....4)run it a couple minutes.......5)put it into all the gear ranges, 6)turn off the engine....repeat steps 1-6 2-3 more times....... also im not sure if those transmissions use a screen filter or a paper filter.......if it is paper then you should replace it before you fill it up the last time. also if you have to drop the pan, if it uses a cork gasket, replace it, if it is rubber and looks in good shape you can reuse it.

all of this is very wasteful and potentially messy for you.......at my shop, we charge $60 for a 4-cyl trans fluid exchange......you will spend almost that much just in fluid if you do it yourself.....especially if you use good quality honda fluid.........AND theres a very good chance you will get coated in trans fluid.