Ever since it opened in 1986, the Xfinity Center has undergone a number of changes, from basic upkeep to expanded seating to a series of name changes that hasn’t stopped many locals from continuing to call it Great Woods a full quarter of a century after that name was retired. This winter, the 24,212-capacity Mansfield amphitheater is set to undergo one of the largest renovations in its history, according to the Xfinity Center’s general manager, Jason Sandoval. Sandoval — who has been GM for the Xfinity