How can I change B1/B2 to work visa?

Your question requires an attorney consultation. It is not a simple question that can be answered on this type of forum. There are many factors that would need to be considered and evaluated. Generally, if you are here on a tourist visa, you are not eligible to work. However, you may or may not qualify under a different type of visa. Since we do not have all the facts, it is impossible to give a meaningful answers. I suggest that you contact an experienced immigration attorney for a face-to-face consultation and give him/her all of the facts surrounding your situation. (S)he would then be in a better position to analyze your case and advise you of your options.