You must following this step.
1.Open your World Editor(WEU,WE New Generation).
2.Click Advanced on top.
3.Click Game Constan under Game Interface
4.Then you search, that called Unit - Maximum unit level.
5.Double click it, or click Edit (Change Value) Button.
6.Then change that value to anythink you want.
Note: Before you edit it, you must check, that called Edit Value box.