It is very important to keep the contact details of your account up to date. You can modify the account contact details by following the instructions below:
1. Log into your account and click the 'My Account' button at the top of the screen and then click on "Settings"
2. From here click on "Edit Account Contacts" under the Edit Account Contacts section of the Account Settings.
3. Update the contact information that you wish to change, and use the tab to navigate the 4 different fields: registrant, administrative, billing and technical. Alternatively you can also check the box "Make all contact information the same as Registrant" to make all the information the same in all 4 fields.
Note, these are the contact details that will be applied to domains registered from within your account. If you need to change the contact details of a specific domain, you can follow the instructions here.