How do I flush or change transmission fluid and filter?

Thank you I will do that. I did not know autozone does the code read free. I'm unemployed due to an on the job injury. I just had surgery Jan. 15,2014 after almost five years 3/25/2009 doi. Waiting for w.c. to approve surgery for a bulged and now deteriorated disk in my L5S1 of my spine. My wife after 15 years raising our 3 children has had to go back to work. And our financial situation is less than up to par and I am trying to save any money I can. This is the only vehicle we have that runs somewhat decent. I'm surprised ot has last this long with just oil changes. For the past 3 years we've had it. She was given a 1996 Dodge Caravan recently from her mother. It was running great up until I went to surgery. And after my surgery drove it home. And it would only go into second gear. And was able to go 50mph. And since then it will omly go 35mph. So the tags are now due onand it has to get smogged. So April the car needs smog and reg May the van I'm curious if both will even pass in current running conditions. Any help and suggestions I do appreciate!