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