Firstly make sure you have it the correct length. The cushioned part is telescopic. Adjust the length so that when you are on your knees your thigh and forearm are parallel to each other. Otherwise when kicking you may miss the pad with the bit of leg immediately above the knee and potentially you could take your kneecap off (Ouch)
Make sure the short "spikes" are free of carpet bits.
To adjust the long spikes, hold the kicker down on the carpet and then turn the dial lowering the spikes until you feel resistance, then give it 2 or 3 more clicks and then the kicker will be correctly adjusted to the depth of pile without puncturing the backing.