Do you have a copy of the Official Guide? If you do, there is a math overview section that basically outlines the math you'll need to know to take the test. Start working through OG's math and keep an error log
. The error log
should tell you which quant area is your weakness (algebra, geometry, arithmetic...etc etc)
If you want to go over the basics, here is a good website http://www.wtamu.edu/academic/anns/mps/math/mathlab/
I would also suggest looking over the sticky posts in this math forum
However, that's just an overview and in order to improve on quant scores, you'll need to participlate actively in this forum and read the answers that are posted and understand the concept.
Hope this helps!