Many newbie ask question about the vape cartridge device.

Here is a Yocan fan's question about How to change voltage of Yocan UNI.

Can't seem to get to 2nd & 3rd power levels, keep trying the button 3 times, getting no where.

Answer:
The Uni is a highly portable device even though the extra features make it a little taller and wider than other 510 batteries in this price range. It also has three voltage settings: 3.4V | 3.8V | 4.2V.

You can tap the fire button 3 times rapidly to change the voltage.
Here are the indicator lights status:
Low: 3.4V, 1 light on
Middle: 3.8V, 2 lights on
High: 4.2V, 3 lights on