Raise the leg rest up as high as it goes using the seat control. Then, inside the right arm rest locate the silver lever with the picture of the footrest next to it. While pressing the lever use your hand or a foot to lift up on the footrest. You'll get it to go up a few extra inches and it makes a huge difference! This works on the BF seats on the 752s and the 762/4s.

(Thanks to doobierw for this tip!)