Open the app,
Switch to the 'Inventory' tab,
Click on a Headset you would like to level up,
In the opened Headset tab, tap on the 'Level Up' button in the left bottom corner.
To level up your Headset you will need KCAL tokens to pay for each level and, optionally, FITFI that you will need to speed up the levelling process. You can find the number of KCAL required for upgrade in the table below:
As the headset’s level increases it allows you to improve its attributes. When reaching a new level, additional attributes will be randomly distributed between Activity, Luck, Balance, and Resistance.
The additional attribute's value for different quality types grows non-linear with each rising level.