The venerable Educational Alliance, which opened its doors to serve Jewish immigrants on the Lower East Side 125 years ago, has gotten a makeover. With politicians, musicians and Educational Alliance board members on hand at the recent ribbon-cutting ceremony, the new six-story, 103,000-square-foot building reopened as the Manny Cantor Center. The $55 million restoration project at the Alliance’s flagship building on East Broadway includes early childhood classrooms, a new fitness center, spacious art studios and a top-floor community space for public events to meet the needs of a changing Lower East Side.