WordPress Tip: Delete Old or Unwanted Plugins
Note: The following is made available under GPL from http://codex.wordpress.org/GPL. It may be edited a little from its original form, but probably not a lot. There is no guarantee this information is accurate…use at your own risk.
Delete Old or Unwanted Plugins — Keeps Your Site Running Well and Increases Security
Many times a plugin doesn’t fit your site or you don’t need it, but you leave it there just in case. These tend to pile up in your Administration > Plugins Panel, making your plugin list long and cumbersome to scroll through. If left there long enough, they might become obsolete with the new WordPress versions and they could get outdated and cause problems–including security vulnerabilities. Check your Plugins list often and clean out the stuff you know you won’t use.
Begin your Plugins housekeeping by visiting the plugin author’s site to see if there are instructions on how to uninstall the plugin via the Plugins panel on the left side of the screen. Some plugins require adding tags and code to your Template files while others require modification of the WordPress administration files. Be sure and read through the plugin’s uninstall instructions to remove each of these modifications so your site will not have errors when the plugin is turned off.
If no specific instructions for uninstalling exist, then read through the installation instructions to check for modifications, if applicable, and reverse their changes, if implemented. If it has been a long time since you used this plugin, you still might have left its modifications in your template files and forgotten them. Carefully remove them.
To remove a plugin, make sure the plugin is deactivated from the Administration > Plugins Panel. Then you can uninstall in that same area. For some plugins, there may be left-over files in your plugins directory even after you uninstall using the admin interface. It’s always a good idea to look in your plugins directory to ensure the plugin files are gone…if not, then delete them.