Bryan Roche, writing at Live Science, says that the idea of a human's IQ remaining the same throughout his or her life is wrong.
IQ tests are designed to "shift" over time so the acquisition of knowledge and skills doesn't really affect it. What my IQ was measured at when I was a child should be roughly the same as it would be if I measured it today, and the test I would be given today would be different from the one I would have taken then.
Roche says that a lot of psychological research suggests that our IQ changes over time -- in fact, it rises. Although we all probably have an upper limit for our intelligence, we can acquire new intellectual skills through study through most of our lives, and most people probably wouldn't reach that limit.
Probably one way to boost the score would be to figure out why I have gotten smarter as I've aged when the only thing I seem to have learned is that middle-aged me knows a lot less than twenty-something me did.