99 5.4 80k on motor 280k on trans

not sure when the tranny was serviced, but how do you tell or know when its time to change the tranny fluid?
i was checking the trans fluid and it looks dirty has a brownish tint to it, and it smells like cow poo.

1,do you do it your-self?
2,drain/change just the fluid?
3,drop pan and change filter?
4, have it flushed at a oil shop?
5, or take it to dealer and have them flush it, drop pan and replace the filter?

 

If you don't know how long the fluid has been in there, change it. Then change it every 30,000 miles.

Here's how to do it. Changing ATF Fluid in a E4OD and 4R100 transmission .: Articles