The trick is knowing that it is a different web site: cancel.1and1.com/.
You can both change your domain items or cancel the whole package here. Log in with your customer ID and password. Click on the Cancellation Button. Click on the Package you want to change. The Cancellation screen gave me the option to cancel my package (all services) or just individual options. I chose to cancel just one domain. After selecting the domain I wanted to cancel I chose “End domain contract” from the drop down list. Finishing the process required clicking some confirmation buttons, then replying to an confirmation e-mail.
Other options include setting a time in the future to do the planned change.