The best advice is to call out a Preferred Doors, LLC establishment who can check it out for you. There could several things that could be wrong. Your electric opener unit may be getting old and the gears need to be replaced. Sometimes, there is an electronic force adjustment you can make on the unit to increase torque to the motor before stalling out. But, this is just a temporary fix and you should find the solution to the actual problem you’re having.
Another cause, and the most likely, could be that you have a broken spring. The spring counterbalances the weight of the door, so that it only takes about 20 pounds of force to lift the door, even though it may weigh several hundred pounds. This is something that requires a professional garage door technician, to replace the correct parts.
Finally, if it’s a sectional roll up door, you might have some kind of binding occurring in the door (the rails, hinges, rollers, or the panels themselves) when the door is opening that prevents it from opening all the way. Maybe you accidentally hit and bent one of the panels and this put the whole door out of skew. Anyway, it would also be best to have a garage door technician out to do this work. It can be expensive (several hundred dollars for a new opener and springs, and a door alignment). Another big plus about calling a profession garage door company, is the service work is under a warranty for an extended length time and you won’t have any more worries about your door again.