I've downloaded several themes to check them out. Some I can 'right click' on and a dialog box opens that I can select 'delete'.... or the little "minus' sign turns black and I can delete it that way. Others when I 'right click' on it it the only selection in the dialog box is 'Duplicate Theme'. On these... the 'minus' button on the bottom stays grayed out. I've got several I'd like to delete but do not know how. Any help would be appreciated.
Thank you!