Wrong forum. This is not a request, this belongs in Wehz.
Some admin move it there please
And the answer is: in World Edit, you open your map and you go to advanced > Gameplay constants.
A smaller window will pop up, and here you enable "use custom gameplay constants". This list contains many constants such as "Hero - max level", which is initially set to 10. You can increase it to 300, though I doubt anyone is bored enough to play it til he's lvl 300...