Go to this page :
Download it then use a software to send it to your calculator (I recommend "tilp", but "ticonnect" do the job too).
Connect your ti83, launch tilp or ticonnect, then send the file ION.83g to the ti83.
On your calc, go to "PGRM", select "ION" (use arrows), then press "Enter".
Once you've done it, a program A appears, this is ION, you need to run this program to launch your game.