Open up terminal. Copy the link of the latest Lua version and download it:
cd /tmp
wget http://www.lua.org/ftp/lua-5.1.4.tar.gz
Extract and compile:
tar -xzvf lua-5.1.4.tar.gz
cd lua-5.1.4
make macosx
Test and install (if test goes through)
make test
sudo make install
And you’re done!