You need to rejet the carb. Install a larger mainjet when you first try to run with this cylinder, to be on the safe side. If it is a fast kit then a larger carb (17,5 or 19 mm) can be reccomended. Also the variomatic (rollers and springs) will most-likely need to be adjusted.
When you mount the cylinder, be sure to put a little oil on the inside with your finger, before you shove it over the piston. Use the proper gaskets (the ones delivered with the kit should be fine).
Final note, I don't know how fast the cylinder you ordered is, but many people on this forum will recommend placing a stronger crankshaft and bearings as the original one might not be calculated for the power a 70 or 72cc might give. You can try it with the original one tho, just don't get unlucky
Edit: A technigas next isn't exactly a 70cc exhaust, so I doubt it will run on its max RPM and power so that lessens the stress on the crankshaft
it can bring down your topspeed a little tho, but it might increase the power in the lower 'gears' of your scooter (because the exhaust will give a lot of counterpressure for your cylinder).