you actually do have a lot of options that you can do.
1.) call customer service (888-294-6804) so they can do the process for you, this will also help you learn what will happen if you change your device. because in some cases, once you change your device on file, your plan will be change as well. so it will be much better if you call them so they can warn you before you do any changes.
2.) My Verizon app/website: you can do it yourself by just logging into your account and you will see that on your profile.
3.) dialing *611. if you are that kind of a person who loves to do the systematic way, you can dial this number and it will ask for your number and would lead you to changing your device.
hope I give you some useful infos