To change the tab titles and many other text headings for your store, you need to access your theme languages section.
 
You can access this by going to Online Store > Themes > ShowTime >Click the  ... button > Edit Languages > English.

A new tabbed interface will open allowing you to set translations for different sections of the site.  

For tabs that aren't visible by default, there is an arrow on the right that you can click to show the remaining translation sections.  

This is where you can find the product page where you can translate the tabs.