Adjusting garage door limit switches can be done easily with a few tools. The limit switches control the travel of the door. When the door does not close all the way, the limit switch may be responsible.
Does the door not close completely or close and then reverse itself? The garage door limit switches may need to be adjusted. It may be obvious when you examine the door what type of limit switches you have. A door opener with a screw drive may have spring loaded switches that shut the motor off when the carriage hits them. Chain drive units may have lugs in the chain that can be repositioned. Some openers have adjustment screws on the unit.
If it is not obvious how to adjust them, find or obtain a copy of your owner's manual for instructions on adjusting the limit switches. Go to the manufacturer's website or try Manuals Online, they may have a copy that you can download.
If the door is closing and reversing you need to set the limit switch so that it stops the door sooner. If it is not closing all the way set the garage door limit switch so that the door goes to the floor. Got them adjusted? Another garage door opener problem solved.