I really don't want to pass the easy levels again for some of the lite games I have if I get the full version. Eg Geodefense lite, physics free, tower madness zero...
I'm pretty sure you can if your jailbroken. I haven't tried it specifically from lite to full. But it should be pretty easy with just renaming the lite file backup to the name of the full version and then restoring the file back to the full. And no it is not illegal at all