No one is telling you that you have to pay for the program again at the very least you would purchase a members area renewal to get new code. Each license comes with one year free to download updates which you have passed.
You can try adding this in bold in index.php near this line at line 15 but I dont have an old version like that to be sure.
Content visible to verified customers only.
If your running a pre 5.0 version you should definately upgrade regardless of what I am posting here because of security issues.