Problem with the categories module

Hello,I has a problem with the categories module.How i delete/untag a reference from the relative category?I can't do it.thanks!
hewei

For a single reference,

For a single reference, double click it to open the editor window. Go to the "Categories" tab, check off the categories. For a group of references, select them and click toolbar button "Categorize...". Select categories and click the Remove button.