You should rev match your rpms if you are going to downshift.For example:Your car @ 40mph in second gear your rpms are at 6,500rpm.If you are driving on 4th geat when your RPM are 3,500rpm and you need to downshift to 2nd gear you should first press the clutch, then gas to rev your car to 6,500rpm then shift into 2nd, release your clutch. Just do all this fast and your car will not jump when you downshift.