Thanks for your KB post.
You can download the software from http://downloads.paessler.com/prtg/prtg.zip directly.
Once you have downloaded the latest version, you can install it directly over the version currently running. The configuration and database will not be affected by installing the newer version over the old and the configuration is automatically backed up before this process.
Please check below links to more information.
Important notes when update from previous version
How do I update software with no internet access
With kind regards,
Chan Siau Hen
Technical Support Team, Paessler AG