need help to delete "key words" used to search files

From: Paul D (prd0844_at_yahoo.com)
Date: 05/31/04 

Date: 30 May 2004 19:12:38 -0700

HOw can I delete the "search words" I have used to search in my
computer. When I search my files for something, that/those key words
are saved and I would like to erase them. How is that done. Thanks
for help