Shimano Cantilever question (BR-R550)

Hi,

I ruined a wheel on my old bike today. I take the wheels out of my CX bike,
put them in my old bike and mount a better set of wheels in my CX bike.

Now the problem: both the old wheelset and the new one are CXP33 rims and I
hoped this could be swapped without problems. But no, the brakes have to be
adjusted. Now the problem: whatever I do, the left brake shoe is closer to
the rim than the right brake shoe. As a matter of fact it is too close to
the rim.

-How do I adjust the brake in such a way that both brakeshoes touch the rim
at the same time?
-How do I get the left brakeshoe to be positioned further away from the rim?

I haven't figured out this braking system yet....

Thanks! Derk