Several parking options are available at the Renaissance Center. Just east of the hotel are the Port Atwater and Beaubien Place garages, each standing nearly adjacent to the Renaissance Center, which is accessible via a covered walkway. Both of these facilities cater to RenCen employees and visitors during the week, but have far greater availability (and lower prices) on the weekend.
Across from the hotel lobby on the West side of the RenCen stands the Center Garage. A fourth option is valet parking, available at the Wintergarden entrance on Atwater Street, facing the Detroit River.
Further details are available via this link, or you may contact the hotel for additional information.