Version 4.15 installer for Windows 8/7/Vista/XP (both 32/64bit)
Download and installation instructions for Mac OS (5.0 or above).
You can also download the desktop client using your phone instead – on your phone open the web browser and go to http://pdanet.co/a
When you run the installer, if for some reason it says the file is corrupted, that would be caused by browser timeouts. Try to download using a different browser or from your phone directly.
You should be able to just install and connect. There is no need for any extra setups. If you are upgrading and you have a paid version, it will remain so even after the upgrade.