This is taken from the knowledge base:
If you have a new iPhone, iPod Touch or iPad that you wish to access your Games With Friends account from, you will need to do the following:
If you have access to your old device:
Launch Words With Friends on your old device
Tap on the account settings button
Enter a new password
If you do NOT have access to the original device:
Set a password on the account using the password reset tool: http://wordswithfriends.newtoyapps.com/forgot_password
An email will be sent to you providing a link to a web page that will allow you to set your password. If you sent multiple requests only use the last reset link that was sent to you.
Once the account is activated as in either of the two steps above, you will be able to access your account on your new device!