To delete a search, click on the seed keyword in the “SECockpit Keywords” tree. In the toolbar of the list, you’ll find the “Delete List” button (aligned to the right) - this will delete the list and remove it from the tree.
To delete multiple searches there is a shortcut: you can create a new "Favorites Folder" and drag and drop all keyword searches you wish to delete (this goes a lot quicker than opening them all). Once you've moved all unwanted keyword seeds onto this folder, click on the folder and Choose "Delete List" in the Toolbar. This will remove the folder and all sub-keyword seed items.