Deleting Recent File Lists

When you create several files in a word processor or spreadsheet or other program, the program will list the files you recently created the next time you start it, down toward the bottom of the File button on the menu. How do you clear the list of recent files? My wife is copying some old audio cassettes to CD. When she is done with each cassette, she deletes the files from the computer but they still show up on the files menu. This bothers the heck out of her so she is bothering the heck out of me to get rid of the file listing.