The electronic structure of a two-electron quantum-dot molecular has studied using the effective mass approximation. The quantum-dot molecular consists of two vertically coupled self-assembled quantum disks in a magnetic field with varying orientation. Based on the calculation, a qubit modulated by the orientation of magnetic field is proposed with the total spin of the system. Electron correlations may lead to the switching of the total spin between S=0 and S=1 states. The switching is realized not by the changing strength but by the changing orientation of an external magnetic field. Our results provide a possibility to use the total spin of the system as a qubit modulated by varying the orientation of the magnetic field. Since high-quality vertically stacked quantum disks can be fabricated successfully, it is realistic to obtain qubits of this type.