Log into your Control Panel and click E-mail at the left side of the page. 

The overview shows a list of your e-mail addresses. Click the Edit button under the desired e-mail address. Change the account type for this e-mail address by choosing the appropriate item from the Please select your account type drop-down menu. 

You can choose This e-mail address is an account, This e-mail address is a redirect or the combination of both. Select the desired option.

If you select This e-mail address is a redirect, the menu underneath it changes. Enter the desired redirect address and save the change. 

If you select This e-mail address is an account with redirects, a new Redirect tab appears in the gray area below. Enter the desired redirect address and save the change.