Steve Kerstein was named managing director of Towers Perrins worldwide retirement consulting practice, which includes design and implementation of retirement plans and asset management consulting. He replaces Robert G. Hogan, who was named managing director-worldwide benefits practice, the No. 2 executive at the firm. Mr. Kerstein will report to Mr. Hogan. Mr. Kerstein had been East Coast regional leader for the retirement consulting practice. The changes are part of a reorganization of senior management after the retirement of several top executives.