The effect of depth and location of a triple-well potential on vibrational resonance is investigated in a quintic oscillator driven by a low-frequency force and a high-frequency force. The values of low-frequency $\omega$ and amplitude $g$ of the high-frequency force at which vibrational resonance occurs are derived both numerically and theoretically. It is found that: as $\omega$ varies, at most one resonance takes place and the response amplitude at resonance depends on the depth and the location of the potential wells. When $g$ is altered, the depth and location of wells can control the number of resonances, resulting in two, three and four resonances. The system parameters can be adjusted by controlling the depth and position of the wells to achieve optimum vibrational resonance. Furthermore, the changes induced by these two quantities in the tristable system are found to be richer than those induced in bistable systems.