A manual adjustment assembly for adjusting the height of a vehicle seat includes mounting brackets for supporting a seat bottom that is movable between a lowered position and a raised position. Separate adjustment assemblies can be installed at the front and rear portions of the seat for adjusting the height of the front portion independently from the rear portion. Or, a single adjustment assembly can be used to adjust the height of either the front or rear portion where the adjustment assembly includes a connecting linkage assembly to correspondingly adjust the height of the other portion of the seat bottom. The adjustment assembly includes a torque tube extends between the mounting brackets and is actuated by an actuator that selectively supplies rotational input to the torque tube. A drive link is supported on one end of the torque tube and is fixed for rotation with the torque tube as the tube receives input from the actuator. The adjustment assembly also includes a spring that operates with the torque tube and the drive link to assist movement of the seat member from the lowered position to the raised position when actuated by the actuator.