Please do not download source code (ZIP or tarball) from here because after the compile engine will contain a bug: if you install it as Xboard/Winboard engine it will play without the hash table (much weaker). Use the following link instead: https://github.com/serg-meus/k2/archive/9797c31576beb51afae98a56e41ad275ffe56d83.zip
If you installs K2 always as UCI engine, there is no difference between versions.