On the page of each person, there is a link that says "adopt this person". When you click this, you will recive an email every year one week before their yahrzeit so that you know when to observe it. The email will be sent to the address that you used to register your account.
If you decide that you no longer wish to receive emails about that person, simply go to the members page and click on the button that looks like "" next to their name to remove them from the list of people you are following.