It's a very straight forward swap, but there's a lot of small parts to consider; make sure you don't fall for the same mistake many people do which is forgetting to change the gear selector mechanism, the six speed one is shorter.
You will also need a Propshaft & New Clutch kit since they're both different are NOT compatible.
Change your prop doughnut and that large bush (can't remember the name of it) between the prop and the gearbox while you're there. grease up the prop splines too. If you can check the condition of the input bearing on the gearbox, make sure it's not got any play in it, probably worth changing just to be sure.
(all these are maintenance stuff you're saving on later, while the car is in bits anyway).