Instructions
Engage Prestige mode by raising your player to the highest available rank, level 70. Entering Prestige mode essentially returns you to rank level 1, strips you of all your unlocked equipment and purchased weapons, and replaces your player emblem. It will be as if you started a new game. The only difference will be that the emblem next to your name in the lobby screen and scoreboards will have been replaced with a slightly more elaborate badge. You can Prestige a total of ten times, and each time you will be rewarded with a separate badge.
Create a new player account on your PlayStation 3 in order to start from the first rank again, without having to level all the way up to level 70. This will have the same effect, but without the "Prestige" badge. This also has the benefit of retaining your original progress on your first account, so you can easily return to the higher levels without having to work your way back up again.
Quit the game and scroll the XMB bar all the way to the left. Locate the "Users" menu and select "Create New User" from the top. Enter a screen name and provide your date of birth, language and country information. Press "OK" to create the account and sign into it.
Scroll all the way to the right of the XMB bar to the "PlayStation Network" menu. Select "Create New Account" and provide the relevant information, including a valid email address. Press "OK" once to create the account.
Ensure you are signed into the new account and launch "Modern Warfare 2." You will start from the beginning at the lowest rank.