1) usually I strap around my neck or shoulder and OFF the power.
2) hold the camera body with the left hand (like what you did in the picture) with the finger on the lens release button
3) with the lens pointing downwards
4) remove the rear lens cap (lens you want to change) from lens B
4) press the lens release button and rotate the lens A to take it out of the mount
5) plug in lens B and rotate to put it into the mound and cover lens A with the rear lens cap.
6) On the power and bring it up and shoot. (assuming you have removed the front lens cap.
Small Little Application Notes:
a) Usually I bring around an extra rear lens cap.
b) Usually I keep all the front lens cap. Only cap it when I have left the place and shooting is completed.
c) Usually I have all the lens hood on the forward position (not reversed).

