Check out the Department of Transport website - it has the guidelines. When I swapped up I was basically ok for 200cc bigger engine than the largest engine to come in that model. Not supposed to go up too much in horsepower either. You want to go more than that you will likely need engineers certification; and that should involve thinks like brake upgrades if that is seen as a necessary part of the change. You will need the obd etc to match the engine too. Expect to have to go over the pits.

B18C type swap is easier as its within the range allowed.