First you need a code, after having it and copying it, or recording it in someway (If you forget one you get, just go back to the 2nd anniversary site and click "My Codes".

Second, you'll need to log on to the server you wish to give your rewards to, which should be your main account because these are pretty good.

Third, you'll need to go to Benefit Hall, which has power packs, level packs, daily packs, daily log in, click the bottom tab, which is "Activation Code"

Fourth, you'll need to input the code by pasting or typing it out, after you put it out, click "Claim" and you'll receive a letter containing your reward.

Fifth, Extract the rewards and enjoy!