You can simply navigate to the location of the data file on your system and delete it.
Deleting a file may permanently remove it from your system, so you may not be able to undo this operation. If you change your mind and are unable to retrieve your Quicken data file, you will have to reenter your data.
Once you've deleted a file, the only way you can get the data back is by restoring the data file from the Quicken/BACKUP folder, where Quicken backs up your data every seven days. Do not open a backup file that you have not restored. If you're sure you want to remove all evidence of your file from a hard disk, use the Delete command on the files in your BACKUP folder, too.