Problem with 1977 Vespa 50R Imported from Sweden

Hello,

 

I have problem with my Vespa what is imported from Sweden.

In Sweden there is two kind of moped-class and mine belongs to moped class II. This Vespa runs only 30 km/h because it is restricted by gearing/transmission. Does anyone know what I have to change to speed up my device? Changing primary gear or what?