Yes as stated by liquidpain above, you can't upgrade the shader model. It's build in your graphics card as a supported technology. It would be better if you provide me the system specs (CPU, Motherboard, RAMs, PSU, Monitor, etc) or if you don't know this just nicely provide the model number of your branded Computer (If it's branded, if not than ask someone that can do it for you) .
If your PC does not have a video card supports Shader Model 2.0, then that indicates that your PC is pretty old.
Video cards that supports SM 2.0 came out in 2003. Current video cards supports SM 5.0. That means your PC may only have an AGP graphics card port which is now obsolete. It was succeeded by the PCI-e graphics port back in 2004.
Please provide the brand name and model of your computer.