Clearing down contents of a listbox / combo box?

I'm moving through a file of employees.

Each employee carries with it information used to populate list boxes within my application.

I seem to be accumulating data, in the list boxes, as I move through my employees.

How do I ensure that I'm populating a 'clean' listbox / combo box for each new employee?

How do I clear down the existing listbox / combo box content prior to loading new data into them or is it easier to it another way?