There are two way to select modes.
1) Type one: Turn on the light. Twist the head (loosen it for 1/2-2/3 turn. You shall see the output changes from high to medium to low.
2) Mode selection type two: Strobe/SoS/Flash etc
a) Turn on the light and tighten the head. Light should be at high setting
b) Twist the head to the lowest level and tighten the head again within 1 second. The light shall starts to strobe
c) Repeat step 2 to access other auxiliary mode.