A lipid assembly composed of a finite number of lipid molecules can have multiple metastable structures. Using a series of coarse-grained molecular dynamics simulations, we evaluate the free energy profile for the transformation of a small vesicle to a disk-like structure called a bicelle. This free energy is found to be lower than that predicted from continuum elastic theory. For small unilamellar vesicles, the relaxation of the internal structure of the membrane is suggested to play an important role in lowering the free energy barrier for the vesicle-to-bicelle transformation.