Great advice from @phoebebebe13 as always! Redeeming your codes will make the worlds' download icon active for you directly from the store, though sometimes it isn't instantaneous and logging out and back should make them show up. And, if you have problems logging back in, you do sometimes have to "reset" Internet Explorer under the advanced internet options AND check the box to delete personal settings.
As far as how to install once you see the download option for them:
Move out all your other .ebc files in the dccache folder and then install so the computer puts them in the 0 file. Then, look at the numbers of the files you moved out. Try renumbering the 0 to one up from the number of your last .ebc file. Then, move the other .ebc files back in and load your game. See if you can load the worlds and see everything you are suppose to see.
I prefer the world installations be among the first files installed, so all my worlds are dcdb0.ebc through dcdb5.ebc. Then, come the compilations, venues, and large sets. So all the single items are installed last. My reasoning is that if anything takes a hit and doesn't load, it'll be more insignificant.