Display the catalogue or a view of the catalogue on the Catalogue screen and use the Clear command button. The catalogue is cleared of all records in the view displayed but is not deleted. 

Note: To delete a catalogue use the Del Cat command. You cannot delete the Standard On-line catalogue.

E.g if you wished to remove all records that are in a particular main topic in a catalogue you would create a view of the catalogue specifying the section to be removed as the criteria in View/find and invoke the clear command.