In the Game Settings, you have a option to request the account deletion but you'll need to wait a month, as the process needs 20-25 days aprox. Once this is done you can login again starting from 0.
Still don't you like the idea of writing a name like, BvB Zero Nine in the place of Borussia Dortmund 09 ? XD
So you can do this and login again the first day from the upcoming season.
Cheers,