Each different software package from RSI requires a separate activation. The activation (master disk) you got with RSLogix500 is only good for that package. When you buy another package, say RSLogix5, you get another master disk with a different activation which you must install in order to use the new package. RSLinx is a bit of a special case. It is included with the programming packages but no activation (master disk) is included. RSLinx will function with the programing packages without an activation and in this mode it identifies itself as 'Lite'. If, on the other hand, you buy RSLinx separately, then you will get a master disk (activation) with it. Depending on how much you paid, after activation RSLinx will identify itself as 'single node', 'OEM', 'professional', or 'gateway'. Each of these have different capabilities. One thing to note here is that there is no difference in the program itself - just how it responds to the activation (or lack of it). So, to upgrade from 'Lite' to any other version, all that is necessary is to install the activation. The only reason to re-install RSLinx is to get a newer version.
One other note of caution - make sure RSLinx is shut down before moving activations for any package.