How do i color calibrate my monitors?

i have never done it before,and i just recently noticed that on all have a little bit(unoticable unless you i look closly) of a colored tint(or something like that) to them,one has a yellowish tint,one has a bluish tint,and the third has a grayish tint.

I first noticed it while playing dirt 3 when i noticed the colors seemed a little off.

How could i go about getting them fixed(easily and free)? 

Windows has its own utility where you can calibrate the colours too, along with gamma, contrast and brightness.