at the risk of sounding like a complete arse. if your asking questions like this you might want to get the help of someone who knows what they are doing. or get someone else to do it! its not impossible, in fact its pretty straight forward but at the same time its not something you want to do on a whim.
it'd be easier to take the complete engine out, swap box onto new engine put back in. you will need to detatch the drive shaft, the exhaust, the wiring loom, coolant hoses etc etc etc. its easier to take it out the front with the whole front end removed. then when its removed it should be pretty obvious what needs to be undone to take the gear box off. good luck!
