Tsukistar

This is my first time posting so pardon me if I messed up - but I'm on the E16 version of Reborn, and am trying to look into where I can get luxury balls. According to the item guide they (in addition to a bunch of other pokeballs) can be found at Critical Capture after upgrading, but how do I go about the upgrading? I tried looking around and wasn't able to figure out much.