The overall power of a unit depends on several components: the character level, the number of stars, the level of equipment, the mods used by the character, and the level of ability development. Below you will find detailed descriptions on how to develop each of these aspects.
There is a general account level in the game. You gain experience points by winning battles and performing daily quests, that will allow you to advance to the next levels of your user account. The maximum available level in the game is 85, and it is important to keep in mind that the current level of the account is the maximum level of character development. To raise the unit level, use the training droid. Enter the Characters section, click on the portrait of the unit you are interested in and then click on Train. Here you can either select the type and number of training droids you want to allocate for the unit, or use the plus at the bottom of the screen to select the level to which the unit is to be trained. Using this second method, the game automatically selects the available training droids to raise the character to a specific level.