No, you can convert your account.
I got that answer from the support:
°°°
The $11 dollar account is the same as the Unlimited DSL account. If you would like to, you can convert your account:
If you would like to upgrade your account, please signup again for your new account on our website.
When prompted for your username/password, do not proceed. Instead, email us your new order number and username and we will convert your account. A pro-rated refund will be issued on your previous order.
°°°
So write the support and they will tell you the same and what you must do