If you want to delete an item from the repository, but keep it locally as an unversioned file/folder, use Extended Context Menu ? Delete (keep local). You have to hold the Shift key while right clicking on the item in the explorer list pane (right pane) in order to see this in the extended context menu.
Delete completely:
right mouse click ? Menu ? Delete
Delete & Keep local:
Shift + right mouse click ? Menu ? Delete