Follow the steps below to change the password of your 1&1 e-mail account through Webmail.
In order to complete this process, you will need to know the current e-mail password. If you have lost or forgotten an e-mail account's password, the 1&1 account owner will need to Reset the E-mail Account Password through the 1&1 Control Panel.
First, log into the 1&1 Webmail 2.0 interface at http://email.1and1.com/ using your full 1&1 e-mail address as the username and the account's password.
Log into Webmail
Click the Configuration button toward the top-left of the page as shown in the image below.
In the Configuration menu on the left-hand side, scroll down and select Extras.
Click the Password link to set a new password.
Click the Password link
Enter the new password once in each text box to confirm that they match. Click the OK button to continue.
Enter a new Password and click OK
Once you have been informed that the change in complete, click the Logout button at the top-right of the Webmail window to log out and then log back in using your new password.
Click Logout then log back in with your new password
For additional information, you may want to reference: