Instructions
Log on to MGO and select the character you would like to get rid of. On the main menu of MGO, enter the Game ID that you initially created your MGO account with and the password in the corresponding boxes. You may have selected the option box that chooses to remember the Game ID and password so you do not have to input them each time. Click on the "Login" icon. Highlight the character that you would like to delete.
Press the "Start" button to delete the character. A prompt will pop up to ask if you really want to delete the character. Select "Yes."
Log on to the Konami ID site to delete your Game ID. On the Konami ID home page, enter your Game ID and password in the two corresponding boxes on the left hand sidebar. In this new window, click on "View/Edit Registered Information," located on the left hand side of the screen. Your account information will pop up in a new window. At the bottom of your account info, click on the small print "Delete Registered Information." A prompt will pop up, ensuring that you really want to delete your account, to which you should click on "Yes." Another prompt will pop up, asking if you are sure that you want to delete, and that the process is not reversible. Click on "Yes" once more. The result will leave you with your other Game IDs and character slots intact, and this particular character slot deleted.