Most part of equipment in the game can be upgraded using the corresponding button in the game storage.
In order to make an upgrade you will need 3 identical pieces of equipment. As a result, you will receive new equipment with one random bonus from a list of possible ones.
We draw your attention to the fact that a received object can have only one improvement. Also worth noting that in case of a second attempt to upgrade an already improved item, the bonus will not be added up, but will be replaced by a new bonus different from the previous one.