You may not change phone number in Coco due to security considerations. If your number has changed, you can do one of the following: 1) Sign in with your CocoID and password. However, Coco can’t auto-match anybody with your new number because your account is still associated with your old number. In addition, when the carrier gives your old number to someone and that person uses the number to register on Coco, he or she will have access to all your contacts on Coco. Therefore, we strongly advise against keeping on using your old number. 2) Register for a new account. Once you have registered for a new account, your address book contacts will automatically be synced to Coco. However, any friends you have added on Coco who are not in your address book will not to synched. You need to manually add them back by searching for their Coco IDs.