Are you talking 4.7 client tools only, or the full K2 server? For client tools you need to check to make sure you are on a supported OS by checking the compatibility matrix. If you using Five with a browser to connect to a K2 server then your desktop should be enough.
But for the full server 8GB simply isn't enough to run the host OS, SQL Server, K2 Server, and Visual Studio in a way that performs well, even if you meet the compatibility matrix. 12GB would be the minimum and 16GB would be better.
As far as downloadable software, you can sign on to the portal to download the installation file. You will need to input your license key to complete the install.