(Reduced, Java-only copy of https://github.com/emilybache/GildedRose-Refactoring-Kata)
This Kata was originally created by Terry Hughes (http://twitter.com/TerryHughes). It is already on GitHub here. See also Bobby Johnson's description of the kata.
The simplest way is to just clone the code and start hacking away improving the design. You'll want to look at the "Gilded Rose Requirements" which explains what the code is for.