Symptoms
Customer wants to disable K2 Site Settings button (and features) on a site collection.
Diagnoses
There is no clear documentation on how to do this and is somewhat unclear on how to do this by using the SharePoint menu system.
Resolution
If you only want certain users not be able to see the "K2 Site Settings" button in the Site Actions dropdown, you could restrict permissions for users or do the following:
Site Actions -} Site Settings -} Under Site Actions -} Manage site features -} Deactivate all K2 Features manually
Also under
Site Actions -} Site Settings -} Under Site Collection Administration -} Site collection features -} Deactivate all K2 features manually
If you wish to completely deactivate K2 on a specific site collection, do the following:
Central Administration -} K2 for SharePoint -} K2 Site Settings -} select Site Collection -} click Deactivate