on the hinges of the doors there is a small plastic cap or caps
once removed you will see an adjustment screw.Use an allen key and turn
the key till you see the door move.
There are usually three hinges on each door ,you will have to adjust each one in turn till the door becomes free.
If your door is in the sun all day and its only catching in the afternoon
wait untill the evening as the doors will expand in the sun.
Im assuming the doors just have one big piece of glass ? If so adjusting the hinges may work but if there is a gap then most likely the hinge adjustment wont be enough. In this case the doors need "toe and healing" which is where you pack out the glass to make the door frame square again.The weight of the glass can make the frame go out of square,measure corner to corner to confirm this.
Once its been toe and healed it should be fine again. google for how to do it as a few guides are out there.
Failure to get this sorted will eventually mean the lock will fail and is the most common reason i see for failure of multipoint locks on french doors.If the lock fails it could means bills of over £200 to get it opened and replaced as some are a real pig to open if failed in the locked position with hooks etc.