Magento has a built-in powerful tool that will help you inspect templates that are currently loaded on the front end. This is very important if your Magento store uses a custom theme or has installed extensions that overwrite default templates.
In the main menu go to System >> Configuration Menu, then in the left side menu click on ‘Development‘tab (it should be located on very bottom of side menu). Once you are in the ‘Developer ‘section use ‘Configuration Scope’ drop down menu and switch to store for which you want to enable path hints. After that, open ‘Debug’ group panel and set both the ‘Template Path Hints’ and ‘Add Block Names to Hints’ to ‘Yes’ value, don’t forget to hit ‘Save’ button or changes will not be saved.
In this link you will find a video explaining how to enable Path Hints in case you didn’t succeed by following instructions from above:http://www.magentocommerce.com/blog/template-path-hints-tutorial-video/
It’s not possible to setup Magento Template Path Hints globally so you will need to choose the store before option appears in ‘Debug’ panel. Once Path hint tool is active your site will look broken, which might confuse your customers and prevent them from navigating normally or shopping in store. To prevent this, use the ‘Developer Client Restrictions’ setting, which is located in ‘Developer’ section. Enter your IP address (multiple addresses can be added separated with comma) and that will limit the path hint tool to the clients with only that IP address, while all the other visitors will not see any change.