You are looking for a driver, because the driver is what implements the API. If you don't have 4.3-capable drivers installed on Windows, you don't get 4.3 support. Same goes for Linux.
Okay guys he has his video card drivers installed obviously, who doesn't, especially if they're programming. He's worried he's not developing using his video cards full potential.
The only drawback to using OpenGL 3.1 instead of 4.3 is you don't have access to a few specialized hardcore features. 3.1 will be just as fast.