Choose the 'Delete field in list' item from the 'FIELDS' menu to display the 'DELETE FIELD' window. Select a field from the 'Fields' subwindow and press the HIDE FIELD> (the field and its entry are no longer displayed in the 'SPECIES/GENE INFORMATION' window) or the <DELETE FIELD> (field and its entry are deleted) button.
A protection level has to be set below the lock icon in the ARB main window, which is equal to or higher than that assigned to the species entry.
An example macro ("keep_listed_fields.amc") is delivered together with ARB, which allows to delete all unwanted fields from a database, by defining a list of all fields to keep. That macro can be found using the file-prompter under ´Macros´ (see EXAMPLES section there).