Now I don't believe that you can, I know that if you wait long enough and just don't use it, the account will automatically be deleted.
How Do You Delete Your Account On Ourworld?
If you don't go on it for a long time it delets it self
As there is no benefit to terminating an account, ourWorld accounts cannot normally be deleted. If you are done playing ourWorld and are concerned about others accessing your account be sure to update your ourWorld Settings to keep your ourWorld info private once you are gone.
Go to settings then hit delete acount