How do you get more memory for xbox360?

You buy it. I wouldn't get memory though. not much games use memory. If your looking to play alot of games get a hard drive ( does the same, but works for most games ) i would order yours online at unclevics.com ( cheapest if you don't mind used .. or new also) and if you want it fast i would recommend a used one at GameStop ( or new) or Walmart.