If you want to uninstall a Joomla 2.5 template you should navigate to the Joomla 2.5 administrative area -> Extensions -> Extension Manager.
Open the Manage tab. Select Template from the Select Type drop-down menu. Search for the chosen template in the filtered results and click on the check box besides it. Find the Uninstall icon in the upper right Joomla 2.5 menu and click on it to completely remove the chosen template.
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