IQ ratings are rising on average, not in individuals, because a wider section of the populous is educated for longer, and more apt to concentrate on activities and occupations that involve pattern recognition and memory. Even those labor jobs, that were once entirely physical, now often involve some sort of pattern recognition or memory. Since IQ tests are psychological and not neurological, they don't test raw intelligence potential, only how the brain is geared toward certain types of tasks, and as a brain repeats a type of task, it'll invariably improve and specialize.
This pattern will continue, as more and more of the world industrializes and shifts to technologies that use those skills, though it'll eventually plateau when the entirety of the population is so trained and specialized (barring a dark age).
Granted, by then, who knows, maybe we'll have cybernetic processors to offload tasks like that to, and our brains will instead dedicate themselves to other, more abstract tasks, that are harder to digitize, and/or we'll be genetic engineering increased intelligence.