If you really want to erase all of the data on a floppy disk, the best and most convenient option is to reformat it. Only do this if you are certain you don't want to keep any of the information. Here's how to erase a floppy disk by reformatting it...
MS-DOS, WINDOWS COMMAND PROMPT
1. Type FORMAT A: and press ENTER.
2. You may need to press ENTER and/or confirm the format, depending upon the prompt which appears.
WINDOWS 95 AND UP (INCLUDING XP)
1. Double-click "My Computer" on the Desktop.
2. Right-click the floppy disk symbol and select "Format".
3. If you're using a standard 3.5" 1.44MB disk, leave the "Capacity" selection on that setting.
4. If necessary, set the "Format type" to "Full" for the most thorough erase, or "Quick" if you just want to erase the files quickly. 5. Click "Start" to begin formatting the floppy disk.
It will take up to four minutes to format, probably less. In the process it will fully erase the diskette, which will now be ready to store new data.