Cellular networks must be updated very often. Due to technical and economical reasons, the complete channel resetting of an urban network has to be done in several steps. We propose a greedy heuristic and an ascent-descent method to reset a network over a given number of periods. All constraints of the channel assignment problem are taken into account (co-channel, adjacent channel, co-site) as well as the resetting constraints such as the number of periods and the limit on the maximum number of cells which can be reset within one step. Some preliminary results are presented on Bell Mobilité data for a network of 359 cells.