Only way is to edit the missions in AlliED, which is now free (it used to be shareware for the full version, but Troy Dangerfield made it free about a year ago).
Oh, and one more thing, I also downloaded the program on a floppy disk but when i used it on a very old computer, it said it still uses shareware. Am i missing something here?
Not sure, but I think only having the "trial" version shouldn't affect your ability to edit the missions in question. You might want to try downloading a fresh copy and installing from your hard disk, though.
EDIT: It might also be date sensitive, so check to make sure the old computer's tray clock reads the correct date.