How to change mail account?

If you use Gmail with your Google Account, it's not currently possible to change your Gmail username after you've registered unless you want to delete Gmail from your account and use a different, non-Gmail address for your Google Account. You can also create another Google Account with a different Gmail username.
If you don't use Gmail with your Google Account, you can change your account username to another email address at any time. Your username is the full email address you used to create your account.
To change the email address on your account, just follow these steps:

1. Visit the Google Accounts homepage.
2. Sign in to your account.
3. Click Change in the Email addresses section.
4. Enter your new email address and your current password.
5. Click Save email address.

Once you've saved the change, you should receive a verification message at the email address you just entered. To complete the change, you'll need to click the verification link in this message. You should also receive a message at your old email address confirming that we've registered the change to your account. If you don't receive the verification email, check your spam folders or request a new email.
Note:

• You can't change the email address on your account to an existing Gmail address, but we invite you to add a new Gmail address to your Google Account.
• You can't change the email address on your account to an email address that's already associated with a Google Account.
• If you want to make your alternate email address the new primary address, you'll first need to delete your alternate email address from the account.
• The account username that you choose needs to be an active, valid email address that you can access.