Including with respect to a tiebreak game.
This question covers everything but the tiebreak: players switch sides after every odd game in the set and after every set.
Within a tiebreak, players switch sides after every 6 points played. At least, that's the case in major tournaments; local rules may differ:
Two different types of tiebreakers -- one used in major tournaments and another sometimes used in United States Tennis Association play -- both require frequent changeovers. The first is the classic 12-point tiebreaker when the set score is tied at six games. The first player to win seven points and be two points ahead wins the set. Players switch sides after every six points. The Coman tiebreaker works the same way except players change sides after the first point and every subsequent four points.