BRITNEY Spears has cleaned up her act. GK Reid, who recently styled the music video shoot for her hit new single, “3,” tells us, “She exhibited amazing energy and was in great shape — her body looked better than it has in years. “She munched on sushi instead of junk food, and even sang live with the words. She worked really hard and was really sweet to all the dancers.” Says Reid of the video, which is an ode to threesomes: “It’s really steamy.”