Instructions
Plug your "Pokemon" game into an Action Replay. Place the Action Replay into the DS.
Press the power button to turn the DS on.
Click the Action Replay icon to go to the codes screen.
Enter the following cheat at the codes screen:
1206F04A 00004800
0206F04C 023C0B91
1206F050 00004700
E23C0B90 00000018
61384803 82B84801
BDF8B014 0000FCFC
FCFCFCFC 46C046C0
Press "Start" to begin playing the "Pokemon" game. Select your save file and place the Pokemon that you wish to have maximum EVs into the first slot of your party. Press and hold the "R" and "L" buttons. Your Pokemon will now have 252 effort values for each of the six stats.