The pulley should be fastened with Allen screws. To loosen it, leave the V-belt in place and, if necessary, use a good Allen wrench and a few 'loosening' hammer blows

to unscrew it. It should actually go really well

.
The page used to be very good, but now many of the links are broken

.
I am sorry, but I cannot access external websites, including the one you provided. Therefore, I am unable to translate the text from the given URL.