Under certain conditions surfactant molecules placed into a solvent form micellar aggregates of various morphology: spherical, cylindrical, etc. These aggregates having sizes of order of several nanometers represent a statistical ensemble of nanoparticles with multiple interactions. The theoretical description of micellar solutions is difficult owing to a high complexity of physical and chemical processes occurring therein. Using the simplified thermodynamic models of spherical micelles, we have studied the relaxation of a model micellar solution to a new equilibrium state after an instantaneous perturbation of thermodynamic conditions (temperature, pressure, etc.). Our numerical experiments allow to distinguish three relaxation stages and to compute their characteristic times. The first two stages correspond to the establishment of quasi-equilibrium states for small aggregates and micelles respectively. The third stage is related to the transfer of aggregates through an activation barrier. This research is the first detailed study of the three-stage relaxation of a micellar solution. The comparison of the numerical relaxation times with their analytical estimates allows to justify the thermodynamic and kinetic theory of micellization which has been developed recently. Our results create a solid basis permitting to calibrate the models of spherical micelles for particular surfactant molecules. Moreover, the experimental measures of the relaxation allow to predict indirectly the internal structure of micellar aggregates.