Renewal is the process by which the Sheriff changes form. When he goes through Renewal his personality and appearance change. Renewal is parf of the life of Spaceslingers. While initially disoriented, a Spaceslinger keeps his/her long-term and short-term memories. The Fourth Sheriff once said "We live to acquire memories"
The exact number of renewals a Spaceslinger can go through is unknown. Initially it was thought to be two. In one episode. the number was 51. Renewal is a survival trait among the Spaceslingers: when a Spaceslinger nears death (or what should be death among other species), their body will expend a large amount of energy to completely transform into the body of a person that spaceslinger has met at some point in their past. They gain the appearance and personality aspects of this person, but not their memories.
Renewal was not part of the initial conception of Sheriff SKY, but was conceived as a novel way to handle it when First Sheriff actor Michael Rennie left the program and was decided to keep producing Sheriff SKY episodes. Since then, Renewal has become part of the plot lines, and a high point of the series, hyped by the producers and anticipated by the fans as a major event in the series.
Showrunner T. David Reston once quipped "When Sheriff SKY gets renewed, the show goes on. When the actor gets renewed, he doesn't."