i want to get some of my legendaries to my white 2
You trade them like normal Pokemon if you go to the Union Room (which is the first room on the left at the top off the Pokemon Center) you can trade them there but you need two DS's.
Another plus side is they can be traded back as long as they stay in Gen 5.
Hope this helps.
You trade between them. All the games from Generation 5 can have Pokemon traded between.