A slow or sticky garage door is almost always a lubrication problem. Dry rollers, hinges, and tracks create friction that makes the door strain against the opener.
Pull the red release cord hanging from the opener trolley. Lift the door by hand — it should move smoothly and stay in place at the halfway point.
Spray lubricant directly into each roller. Apply to each hinge pivot point. Wipe the inside of the tracks with a rag then apply a light coat of lubricant to the inside surface of each track.
Check all bolts on track brackets and hinges — tighten anything that's backed off. Re-engage the opener trolley. Press the opener button and watch the door move smoothly.
If the door is slow because a spring is broken or stretched, do not attempt to replace garage door springs yourself. They are under extreme tension and can cause serious injury.