Tower of Time

At the end of the second level you get the blueprint necessary to upgrade the armoury a second time. This is necessary to upgrade a champion (in this case Kane) to level 6.

Improving the armoury and upgrading the champion costs a lot of gold. You will find gold lying in the corners of the level. You will receive gold for battles. Another very good source of income are the challenges. You can find them by selecting the tower in the city and changing the tab there.

You should be able to get this toward the end of level 2 of the tower. That's when you'll find the second blueprint for the armory, which will allow you to get Maeve and Kane to level 6. Once you find and buy the armory upgrade, it's just a matter of getting enough gold to buy the level-ups for the character of your choosing.