In the Administration Back End, you can navigate as follows:

1. Mambots (menu) -> Site Mambots

Option A - Disable Discussbot
2. Select the "Joomla-SMF Discussbot" check box
3. Click on "Unpublish" at the top

OR

Option B - Change Options
2. Click the "Joomla-SMF Discussbot" link
3. Select the options that suit you best. From here you can disable Automatic DiscussBots, Change the Image and carry out other stuff. Most of the options have ToolTip style help if you hover your mouse over the option captions.