In different scenario, this question can be different. In fact, this question can be seperated to several questions:
The most important thing is backup your previous configuration files.If there is any exception during the upgrade, we can roll-back to previous version.
All miniSipServer configuraion files are stored in the 'config' sub-directory where MSS is installed.So it is very easy to backup the system, what we need do is just copy this sub-directory to anywhere your want.
We can uninstall previous version and install the new version in the same directory.Because the configuration files are kept in the 'config' directory, the new version will detect, use and upgrade previous configuration files automatically.
Yes, of course. By default, it is free to upgrade MSS from low version to higher version since they can share the same license. So just download the latest version and enjoy it.
First, you need download new 50 clients version from our website.
Since different licenses are used, you need pay the price differentials between these version. Please visit our 'buy now' page to get details.
Once you get the new license, you can uninstall previous 20 clients version and install new 50 clients version, then input new license to enable it. The upgrade process is almost same with above description.