One of the founders of the AOL Time Warner conglomerate is trading up for bigger digs in Miami. Caesar P. Kimmel, a co-founder of Warner Communications with the late Steven J. Ross, has sold his 3,140-square-foot, three-bedroom condominium on private Fisher Island for $1.59 million. Now he's moving to another spot on the island, a luxury retreat that's accessible only by ferry, yacht, helicopter or seaplane. Mr. Kimmel's new residence has four bedrooms, 3 1/2 bathrooms, about double the square footage of the old place, views of the Atlantic and downtown Miami and an interior that was designed by Ted Fine. The sale price: $3.75 million. After leaving Warner's in 1984, Mr. Kimmel, a longtime owner and breeder of thoroughbred racehorses, has spent time in the gambling business, owning casinos in Antigua and Russia. His Fisher Island neighbors include actor/director Mel Brooks and his wife Anne Bancroft. Jill Eber and Jill Hertzberg, of Coldwell Banker in Miami, handled both of Mr. Kimmel's transactions, as well as Bee Gee Maurice Gibb's recent $7.2 million purchase.