Sears garage door opener only open half way going up..

This one is easy...there inside your garage door opener, the one on the top of your ceiling in your garage has little like knobs ..mine has a straight like screw driver circles attached to knobs. Round dials with screw driver like knobs on top of them...they are adjustable. your "tune" them until they just stop where you want them, don't forget to grease your chain, keep your tracks clean of dust, and make sure your safety "stops" are working properly so that if children are in the way, it will stop. Also..make sure there is nothing in the way of the track. If the sensor "senses" a block...that will also cause it to stop halfway. Now if you could tell me how to change my combination on my keypad...I'm all set.