Naturally 3CX will expect that you only run one instance. The Enterprise edition is required if you want to keep two instances (fail-over option). You can activate the same key more than once (to briefly prepare for an upgrade), but be aware that every time to register your key on a different computer this information is captured and carefully monitored by 3CX. I would suggest you make a call to 3CX Technical Support to see if you have any activations remaining on your key. You don't want to run out of activations while performing the upgrade during hours where no technical support is available. Don't forget that changing the 3CX IP is a bad idea. So, backup the original server and turn it off. Then start the new server with the correct IP address, and reinstall the server on the new server. Further, things can get messy with the Web Conferencing service too if you have two computers with different FQDNs registered with the same key. I should also point out that I've had some really screwy things happen when you have multiple 3CX servers running in the same local subnet. You either need to isolate the old and new servers, or you should turn the old one off before working on the new server. My preference when upgrading 3CX is always to keep the original server intact as a fall-back option in case the upgrade doesn't go well. Sorry, that's a long answer when I could have simply said "yes" you can do it.
