After you open top cover, you will see 3 pin connector with "L1", "L2", "N" pins.
L1 - half speed (50%)
L2 - full speed (100%)
N - neutral
For to use your fan on I speed (50% of power) connect brown wire to L1 and blue wire to N pin.
For to use your fan on II speed (100% of power) connect brown wire to L2 and blue wire to N pin.
Do not connect wires to L1 and L2 pins in same time!
It will broke your fan.