Here are the steps, to change your e-mail;
Step 1: Login by clicking the 'Login' button on the upper right corner of the screen.
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Step 2: Login using your in-game nick and password.
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Step 3: Click your nick on the upper right corner of the screen, you'll get a small pop-up and click 'Update Profile' in that small pop-up.
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Step 4: Change your e-mail address by deleting the earlier e-mail and typing the new e-mail which you want, then you can change your password using the new e-mail.
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Hope this helped.