Every software has its bugs. What's more - these bugs are often discovered after the official release of the product.
So, You have spent your money to create fancy box, to record CD-ROM's and to distribute Your software and several days after - THEY appear. You are getting bug reports from Your users (some of them seem to be very angry). What to do? Will You record another CD-ROM with corected version of your program?
No.
You should create and distribute the "patch".
By "patch" we mean the file containing description of changes You have made to Your product since the official (or just previous) release. All the files You have modified, added or deleted will be described within the "patch file". What's more, modified files are stored as difference between previous and current version to keep the patch files as small as possible.
After creating the patch, you can distribute it to Your users to repair bugs or to introduce new features (as a bonus for Your users for example). With the patch You will have to distribute the patching program LFPATCH.EXE (included in this package and royalty-free). LFPATCH will read the patch file and update old user's installation to the current version of Your product.
Distributing the changes as the "patch files" has several significant advantages over distributing new version of the product. First, You don't have to make new CD-ROM's (or multiple floppy disks) and new boxes. The patch files are usually small and easy to distribute on single floppy or over the Internet. Due to the differential nature of the patches, You can also distribute Your patches freely (from Your Web page for example), because it is impossible to install patch without previous (bought and registered) version of product.