A STANDARD TRANSMISSION IS THE EASY ER ONE TO DO . AN AUTOMATIC is a whole new
situation ,and if you don't have the proper tools like a transmission jack ,and spline tools to line it up when reinstalling it you could damage the o rings in the spline seals that keep it from leaking ,once this happens you'll have a big hardship to deal with like the guy says take it some where.
If you are asking this question online, it probably means you don't know how to work on cars. A transmission job is a very specialized and skilled work, and usually you have to take your car to a special transmission shop to get it replaced or repaired.
Unless you have all the tools and are a super-learner, I would suggest you rather go to a local transmission shop, or sell your car for any amount because it might not be worth it.