Within the Product Editor, click the Descriptions tab. Five sub-tabs will appear that you can click on, one for each description.
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You can rename the tabs on an individual level in the Product Editor or at the global level through Theme Settings. Go to Themes > Edit Theme and select Product Details from Catalog Pages in the left-hand navigation.
Renaming the tabs here is a global change that will effect all product across your site. This change will be visible on the front end and in the Product Editor.