Fist step is loosing the A1 screw. (A1 and B2 can replace with each other. They are the left screws)
And then loose the A2, B2 and B1 screws.
Pull open the nut by hands. Please check if the upper nut is loosed or not.
If you want to tighten the preload
Locking the A1 screw is the way to tighten the preload. So is locking B2 screw.
Fix the lower nut and turn the upper nut with counter clockwise direction (if it’s left helix, please turn clockwise) and then turn all set of nut to find the preload you want. When you find the preload you want, please lock A1 screw until you feel the screw is touching the fixing key (notice that the A1 screw can’t be too tight or it will influence the smoothness and tolerance of the nut)
Please check the preload again. If the preload is missed, please repeat the steps above again.
And then, please lock the B2 screw until it touches the fixing key. It’s for holding the nut (Please notice that it can’t be too tight, either)
Finally, lock the B1 and A2 screws until touching the fix key (please don’t be too tight)