New documentation available at https://docs.openkm.com/kcenter/
The documentation at the https://www.openkm.com/wiki is definitivily deprecated.
Consider only use it, if you are user of OpenKM version 6.2 and older.
Click in the banner to close the warning.
Select some filebrowser rows.
Execute the action delete will be shown a confirmation popup.
Click Accept button. All selected rows will be deleted.