Permanently Deleting a Quick Style

Further to what has already been mentioned, a Quick Style is nothing more than a Style which has the option set to make it available in the Quick Style Gallery on the Home tab. If you simply want to remove a Style from the Gallery you need only right-click it there & select the Remove from Quick Style Gallery command. That will remove it from the Gallery but it doesn't delete the Style. Alternatively, you can go to Format> Style, select the Style then click the Modify button & clear the check on Add to Quick Style list.

Among other ways to go about it, you can delete a Style from a document by clicking the dropdown button adjacent to the Style listed in the Styles pane of the Toolbox & selecting the Delete command [if available], then confirming the deletion. The deleted Style will be removed from the Gallery as well. As Andrew indicate, that will not delete the Style from the template on which that document was based [assuming the Style was saved to the template in the first place :-)... Styles can be document-specific].

If the information given isn't sufficient, please provide a more detailed description of what your specific objective may be. It would also help to know what it is that you've "read" & "tried", which Styles you're referring to, as well as how your efforts failed to attain that objective. These Word 2011 Help articles may be useful:

Apply, change, create, or delete a style

Apply, change, create, or delete a Quick Style set