Nike, I think there is a "typo error" on the drawing within the motor's symbol. U2 should be W2, V2 should be U2 and W2 should be V2. In the Delta connection, as you can see L1 voltage is on the same motor winding leads(U1 & U2) w/c is abnormal in any 3 phase motor configuration,likewise with L2 and L3 line voltages.
For a constant supply line voltage, you can never alter the speed of a 3-phase motor unless we have a VFD control or dual voltage motor.