Which type of account are you referring to, a user account or a forum account? If you have a forum account you no longer wish to use, simply click on your forum avatar (top right of any forum page) choose My Profile, go to Settings and find the option to "Delete Account".
You would normally only have a user account (with Magix) if you have previously purchased something from their product range. So, have you previously purchased a software item and now no longer have it or use it, or...? I do not think there is any way for you to delete such an account.