If you are receiving the following error.

Destination folder already exists. /home/public_html/wp-content/plugins/plugin-name/

This means that WordPress began the installation process, but failed to complete for whatever reason. Because the plugin does not contain all the files, WordPress doesn’t recognize the plugin as valid, so you can’t delete it through your dashboard. Because the folder exists, you can’t install the same plugin and overwrite the existing folder. The only way to fix this problem is to FTP into your directory and delete the plugin folder.