1. Click Extensions > Plug-in Manager.
2. A list of all installed plug-ins will be viewable. You can disable a plug-in by clicking the Green Check Mark. (See the image below).
   
   
3. Once you have selected the green arrow is should change to a red circle showing that the plug-in is now disabled.

Disabling a Plug-in in the PhpMyAdmin Interface
In the event that there is an issue with disabling a plug-in through the back end of the Joomla site, these instructions explain how to disable it through the database using phpMyAdmin. While in phpMyAdmin you can also disable modules, extensions, libraries. Refer to How to Access PhpMyAdmin.

1. While in phpMyAdmin select the jos_extensions table. After selecting the table you will need to select the SQL tab and run a query (listed below).
   SELECT *

   FROM `jos_extensions`

   LIMIT 0 , 300
   This query will select all of the content in the table jos_extensions.
2. Locate the plugin that you wish to disable. Once you have located the plugin, select the Pencil button or Edit button to edit a specific table field (see image below).
   
3. Now that you are on table field view scroll down and locate the enabled field. In the enabled field change the Value to 0 to disable or 1 to enable (See the image below.)