Sorry for asking such a stupid question, but how do you upgrade your forces? And I'm not talking about promotions. I'm talking about upgrading a Warrior army, into a Legion one. Thanks in advance. :3

Please check the forum, there are many post regarding this. Anyway, if you are a German, you unit will upgrade as soon as you discover the tech that unlock that unit, or Build Leonardo Workshop, but with this only works once, so make sure to build it at the right moment.

If your German Unit is ELITE, then it will upgrade, but I hear its Ancient Era only. Leonardo's Workshop works great,too :]

Its an Ancient Era BONUS which means you GET it in the Ancient Era but it applies for ALL eras.

But the general rule is you can't, there is no 'normal' way to modernize troops.