The stroke (the amount it sweeps) can't be adjusted.
But, to adjust the park position, lift the arm away from the glass and pull out on the small tab at the base where the arm attaches to the shaft. The tab will release the arm and you can slide it off. Put some anti sieze on it when you reassemble it, they have a tendency to sieze on after a few years.
Also, you might need to open the hood to get the arm on & off.
Hope this helps!