Pretty easy, but you should plan to jack all four corners so the car is level when you fill. Tip: take out the top fill plug first, just to be sure you can get it out with no problem, before you dump your fluid. Use chalk or white out etc to mark the plugs before removing so you know about how far to tighten back in to factory spec.

Takes longer to jack the car than to change the fluid. I've done it twice in 40K miles. I am using Amsoil Syncromesh MTF. They sell a pump that also attaches right to the top of the quart bottle to do the refill easily.

No more difficult than doing an oil change.

 

I have an '06 GT 5-speed. I recall that the fluid was supposed to be changed every 30k with ATF. I did it early because i like synthetic stuff, and I've done it at each 30k mark since. You need a 3/8" drive to take out plugs, don't even need an attachment. I did mine the old fashioned way, got underneath and pumped the fluids in. Makes me nervous the thought of taking ATF into car's cabin, wouldn't want a spill!