So let’s say you just purchased a Kwikset entry lever from Lowes. You manage to get it installed and even get the levers in correct orientation. If you are lucky the keyhole will be correctly oriented so you can insert the key with the teeth up. If you are not so lucky, the keyhole will be upside-down so the key goes in with the teeth down.
Allegedly the lock will still work even if the tumbler springs have failed, if the keyhole/cylinder is oriented so the teeth go in up so this is the desirable orientation. The directions included with the entry lever do not tell you how to do this.
Fortunately, Kwikset has a video on their website that shows how to reverse the cylinder. There is a small clip on the cylinder you can push/pry out with a small flat-head screwdriver. You then pull the cylinder straight out, rotate it 180 and then push it back in and re-install the clip.