We have the replacement tank, same model installed by professionals 9yrs ago. However, we don't understand the plumbing as it attaches to the tank itself! The pipe T's into the water pipes, perhaps by a free spinning joint? We are NOT plumbers, and because this unscrewing/screwing would possibly unhook the elbow etc. attacted to the tank itself, we think this must be reverse threaded farther on?
Hard for a granny to describe... if we could just get the old tank REMOVED we could perhaps figure out how to slide the new one in place!
But arg, we are so frustrated... any suggestions? Our problems are ONLY those plumbing parts! Oh, please, HELP!!

This site might help.

Replacing A Pressure Tank On A Residential Water Well System (http://www.hammerzone.com/archives/plumbing/well/pressure_tank/replace.htm)

I would think you have a union to disconnect. The site above has a pic about halfway down illustrating that.