The market security code is necessary to protect your transactions in the market in case of unauthorized access to your account.
The code management menu can be found in Settings -> Account.
To change the code enter the current code and the system will prompt you to install a new security code.
If you forgot your code please make sure the account is linked to your email, and the email login is verified. All this can be done in Settings -> Account. As soon as the mail is verified, go back to Settings -> Account, select CHANGE or DISABLE in the security code section, then FORGOT THE CODE and confirm sending of the new security code to your mailbox. Follow the instructions in the email to change or disable the code.