SIMPLE ANSWER.... YOU DONT!
More in depth answer. The bedknife is fixed to the frame, you cannot adjust it. You can however adjust the reel. There are 3 1/4" bolts (7/16 head) on each side of the reel. The side with the sprocket is held with nuts the other side is just thread into the bearing holder clamp. Loosen these bolts about 1 turn. Then on the inside of the frame if you look at the bearing holders there notches, take a punch and hammer and tap them forword. The bearing holders are oblong so when you turn it forward it will bring the reel closer to the bedknife. It works best if you take the reel chain off. You want it to just barely make contact with the bedknife. You should be able to cut 1 thickness of paper all the way across. Although 4 thicknesses is generally acceptable.
If it does not cut one 4 thicknesses of paper you will need to back lap or sharpen the reel. PM me if you have any questions.