Apollo Global Management is promoting two top executives, taking a step toward solidifying a succession plan for Chief Executive Marc Rowan. James Zelter, 62 years old and co-president of Apollo’s asset management arm, will become president of the holding company that also includes insurance company Athene, the firm said Wednesday. John Zito, the firm’s 43-year-old head of credit, will take Zelter’s place as co-president of the asset management arm alongside Scott Kleinman.