Sorry I thought this said "How do I trade my Kyurem Black and White from Pokémon White 2 to Pokémon X and Y." - In fact I'm pretty sure it did.
Nevertheless you can't trade Kyurem Black or Kyurem White to Pokémon Black or White. As a matter of fact you can't trade Kyurem fused with either Zekrom or Reshiram at all.
Kyurem Black and Kyurem White were not developed when Pokémon Black and White came out, and because you can't trade them fused you cannot get them in Pokémon Black and White.
You can trade Kyurem, Zekrom and Reshiram individually from Pokémon Black and White 2 to Pokémon Black and White, but you can't fuse them together as the DNA Splicers (the item needed to fuse Kyurem with either Zekrom or Reshiram) was not available in Pokémon Black and White, henceforth you can not get them in the game.
Source: Experience and Knowledge
Hope I helped :)