Note: This applies to publisher accounts only. If you are not sure what panel you are logged into, look at your url and see if it says Https://publisher.admailr.com 

Once you are logged into your panel go to Customize - Category from the main menu as shown below.
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Once you have clicked the category sub menu you will then see all the categories that can be shown in your newsletter. 

To see the sub categories of each category you must click the plus sign next to the main category name as shown below. 

Once you are done selecting or deselecting your categories you will need to make sure you click the save button on the top right side of the page.