Andy Bechtolsheim, a revered technologist who cofounded Sun Microsystems and has been instrumental in designing the company’s servers, is stepping down from his day-to-day role to help build a new networking startup. Santa Clara, Calif.-based Sun, which makes servers and software widely used in corporate computing centers, said Thursday that Bechtolsheim’s transition to part-time work status was effective immediately. He will give up the title of chief architect but will still play an important role in product design, the company said.