Extensions Menu > Click Extension Manager
Upload Package File > Click Browse > Select plg_webmastersiteverification_v0.2-J25 > Click Upload & Install
You should then see a notification from Joomla 2.5 that the plugin has successfully been installed.
Extensions Menu > Click Plug-in Manager
Filter for Webmaster Site Verification and click it.
Change Status from Disabled to Enabled
Then on the right side of the page under Basic Options enter your website verification IDs, and then click Save & Close which can be found at the top of the screen on the right.
Then you might need to clear your cache, browse to Site Menu > Maintenance > Clear Cache > Check Box com_plugins or check all followed by clicking the Delete button found in the top right hand corner of the screen.
- How do I know if it's working?
Simply head to the root of your site as a normally visitor and check the source code to ensure the plugin is correctly working as intended.
It should look something like this
Removal or Disable
Extensions Menu > Extension Manager
Click Manage on the sub header menu
Filter for Webmaster Site Verification and check its box followed by pressing the uninstall or disable
Download and Support
The download and support page can be found here Webmaster Site Verification