Steps

1. Open the Files tab and find the oxide/plugins folder.
   
   
   
   
2. Use the Upload button or drag and drop the file.
   
   
   
   
3. When using the Upload button, select the plugin file and click Open.
   
   
   
   
4. That should be it! Make sure you keep the name as it should be (without (1)) and the server will load your plugin.