Q: how do i update my software on ipod touch 1st gen

I found my old iPod Touch first generation which did not work anymore.  I traded it at the apple store for a reconditioned iPod Touch 1st generation but i can't add apps to it.  This is for my 4 year old so I need to get it working.  I also can't find a way to update the operating software only os 1.1.5.  I'm really disappointed because no one even really helped me at the apple store!