Intelligence is also malleable through thinking and learning. I remember reading the story of a black kid who was on trial for murder. His IQ was measured at 64, which was below the 75 required to be eligible for the death penalty.
However, after having spent 6 months with his attorney and having them continually explain legal concepts and his case, his IQ was later measured over 80, which made him eligible for the death penalty.
I once took two IQ tests on the same day.
One: 133
The other: 167, which is stupid high. Due to peculiarities of the test for me, it was inaccurate.
Tests vary. But I can assure you that the consensus of psychometricians is that IQ, properly measured, cannot be significantly raised after early childhood, if then.
We do know a bunch of ways, however, to bring IQ down.