It is possible to promote units from one level to a higher level.

For example, from T1 to T2 and so on to T11.

There are several advantages:

• Increases the power easily
• It is taken into account in the daily quests “Train XX units”.
• Facilitates the management of units during events and attacks: You don't have to manage T1, T2, T3…
• If you already have T1, it requires less resources to promote them than to create new T2

You have to go to the unit building you want:

• Warriors camp
• Shooters camp
• Vehicle deposit
• Riders camp

Then go to the units to be promoted and click on the little arrow in the upper right.