You should pull up and remove weeds by hand as and when they appear. If it is a regular problem, you might need to reseal the paving. In extreme cases, the sub layer itself may need to be re-laid. You can use weed killer, however some paving can be discoloured by stronger weed killers.
Dunbeath
Dunbeath is a village in south-east Caithness, Scotland on the A9 road. It was the birth place of Neil M. Gunn (1891-1973), writer of The Silver Darlings, Highland River and so on, a number of whose novels are embeded in Dunbeath as well as its Strath. Dunbeath has a really abundant historical landscape, the site of various Iron Age brochs as well as a very early medieval reclusive site (see Alex Morrison's archaeological study, "Dunbeath: A Cultural Landscape".) Of Dunbeath's landscape, Gunn composed: "These small straths, like the Strath of Dunbeath, have this intimate appeal. In boyhood we learn more about every square lawn of it. We encompass it physically as well as our memories hold it. Birches, hazel trees for nutting, swimming pools with trout and a periodically noticeable salmon, river-flats with the wind on the bracken and also vanishing rabbit scuts, a wealth of wild flower and tiny bird life, the soaring hawk, the unforeseen roe, the old graveyard, thoughts of the people who as soon as lived far inland in straths as well as hollows, the past as well as today kept in a minute of day-dream." ('My Little Bit Of Britain', 1941.). There is a neighborhood museum/landscape interpretation centre at the old town college.