Disable Via Joomla's Files
It is also possible to disable a plugin via the files. Login to your file manager and access the root of your Joomla files. You should find a folder called /plugins/
The next step is the trickiest - the plugins are divided into different folders. If you don't know Joomla well it might take a little searching. However, if your plugin is causing real problems on your site it's highly likely to be in one of these three folders:
Each plugin has at least two files: pluginname.php and pluginame.xml. Most will just have those two files, some will have a few more.
However, to disable the plugin all you need to do is remove or rename the PHP. If I wanted to disable the Joomla plugin, I could rename joomla.php to joomla.php-off: