Locked out and email full

My cpanel email address sent a message saying it was 80% full so I have tried to log in and clear it out. Problem is I can't remember my password. So I have clicked through the 'forgotten password' process and guess what, it sends the password reset email to the account that I can't access because the email box is full. I am completely non-techy and have no idea how to resolve this now. Any help?