Renaming the tabs via the language file.

 The titles for the tab triggers are rendered using strings from your template's language file. 

The language file for any Joomla template is normally found in the following folder:

language/[your language]/tpl_[your template].ini.

Add the following strings to your template's language file and adjust accordingly.

TABLEADING="Leading"
TABPRIMARY="Primary"
TABSECONDARY="Secondary"

If you paste the code in your language file then you should see the tab title triggers changed as per the screenshot below.