Within the Product Editor, click the Descriptions tab. Five sub-tabs will appear that you can click on, one for each description.
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.