How to deactivate Banner Manager

Please Help.
Somehow, some way since i installed the Banner Manager i seem to get a “Http 500” warning whenever i try to access the “Installed Plug-in” panel at the back end of my website. I can’t seem to access the “appearance” panel either. website is http://www.basketballclubsarnen.ch/
I really need a way to deactivate this Plug-in without using the “installed plug-in” panel.
Thanks a lot

https://wordpress.org/plugins/useful-banner-manager/