How do you upgrade pixel shader

Pixel shader technology is hard-coded into the video card and its drivers. If you have a very fast processor and a good amount of ram, you may be able to get around the pixel shader requirement by downloading "3DAnalyze" or "Swiftshader 2.0" to emulate pixel shader.

More likely, the best option is for you to simply replace your video card with one which has native support for pixel shader.
Video cards with pixel shader 3.0 are very common these days, it is not an expensive upgrade & will improve performance on other programs as well.