You can upgrade your hero characters by tapping on the hero icon on the menu shown in the map screen, or by tapping on the watchtower building next to the army standing beside your castle.

Most upgrades will require "battle banners" which can be collected as loot when attacking the orc camps.

Some upgrades will also require special tokens. These are unique to each hero and have an image of the hero they are for. These can be earned when attacking orc camps or purchased from some special offers.

As you upgrade your hero characters they will gain more attack power, more energy and an increase of their special ability.