Since MainWP Dashboard version 4.3, MainWP Extensions can be removed directly from the MainWP Dashboard.

1. Navigate to MainWP Dashboard > Extensions page
2. Find the Extension you wish to remove
3. Click the Disable button
   
4. After the page refreshes, click the Delete button
   

Extensions can also be removed like any other WordPress plugin. To remove Extensions in that manner:

1. Login to your MainWP Dashboard site
2. Go to the WP Admin > Plugins page
3. Find the Extension(s) you wish to remove
4. Deactivate it
   
5. Delete it

All MainWP Extensions will completely uninstall themselves, so there is no need to access your server via FTP to manually delete extension files.