Use xDelta UI to patch your clean (i.e. no anti-piracy patch has been applied) Black 2 or White 2 ROMs with the appropriate patch of your choice. The way to do it should be fairly self-explanatory.

Complete version includes all changes. Vanilla excludes the following:
- Any Pokémon changes except for compatibility with the three new TMs.
- Changes to Level Up movesets.
- Changes to Attacks.
- Certain trainers have their moves changed since they don't gain the new techniques they would in the Complete version.

The CRC32 for the ROMs should be as follows (this is viewable in WinRAR):
Pokémon Black 2 - 8A42D36E
Pokémon White 2 - B72BBA42

ROMs that are already patched will probably not be patchable with the BBVW content, though I'm not 100% sure.

The filenames for the ROMs in question should be:
Black 2 ~ iRiL-PkmnB2.rar
White 2 ~ mwl-pkmnw2u.rar

You'll have to find them yourself, though. Alternatively, back up your real cartridges!

Hopefully it works out for you. Happy playing!

- Dray

P.S: Those of you using no$gba/zoomer should probably check out this link:

http://forum.romulation.net/index.php?topic=60304.0