I am getting ready to change engines in my 2000 chevy venture not sure if comes out from top or bottom.

Bottom. You have to unbolt just about everything from the block, unbolt the subframe, lower it, then lift the rest of the vehicle over that. This assumes you don't have a car hoist already. Not a job for the faint of heart or many shade tree mechanics.

I just changed the engine in my 1999 and took it out from the top. it is a very tight fit but will work.