The code comes by email, but I can't activate the code to access my account in the game on the website as the email description says to change the game password; it is not appearing.

Hi, this is what you do:

1) Visit details page
2) Click: send email with a new unlock code
3) Get email
4) Paste code from email into LFS "GAME password"
5) Click unlock

The "GAME password" field you will find in LFS unlock screen. This is accessible by a button at the bottom right of the LFS entry screen.