Forge and upgrades (>+1?) (fr)

Hello there!
Sorry for my very bad english.. (I'm french..).
I'm playing Carthage, and I'd like to upgrade my units. The forge can only add 1 level of upgrade (bronze), and I would like to upgrade more! (silver, gold, diamant.. ah sorry it's not minecraft ^^).
Among the build tree, it seems we can't upgrade the forge itself so I think it's not possible, but I'm even asking.

Well, You can edit EDB file in data folder. Open it and look for blacksmith. Change the number 1 to 2 . Save and exit then load your save. If you do it right you can train or retrain unit with silver blade and shield icon. If you change the number to 3 you should have gold icon.