EnterraHost
To update your billing details, open Account settings from the gear in the top bar or the sidebar, and edit the card headed Your details. There is one Save details button for all of it, so change as much as you need in one pass.
These are the contact and invoicing details on your account. They are not card details. A saved card is a payment method, and it lives in the checkout where it was entered rather than on this form.
What you can update your billing details to say
First name and last name share a row. Company name sits under them, behind a link reading Add company details, and is the one field you can leave empty. If you have never filled it in, the link is a single extra field rather than a hidden section.
Then the address, in the order a form usually asks for it. Address, Address 2, City and State or Region, Postcode, Country. Address 2 is the only optional line here. It is for a suite, a unit or a floor, and leaving it blank is normal.
Mobile phone number is last, with the dial code shown beside it. The code follows the country you have selected rather than being editable on its own, which is the same rule the sign-up form uses.
What is required, and what happens if it is missing
Everything except Company name and Address 2 has to be filled in. Save with a blank first name, last name, address, city, state, postcode, country or phone number and the form refuses rather than storing a half-complete record.
There is a reason it is strict. Your address is what appears on an invoice and it is used as a contact record for a domain you register. An address that arrives half filled in creates an invoice that cannot be sent anywhere useful and a domain contact that has to be corrected later, which is harder than typing it once.
What the details are used for
The address is the invoicing address. It is printed on the invoices your account issues, which is why the fields are laid out the way they are rather than as a single free-text box.
It is also the registrant contact for a domain you register with us. That means a change here reaches the contact record attached to the domain, and anything that depends on that record follows it.
The country decides two things that are easy to miss. It sets the currency and the payment method your account uses for new orders, so moving the country changes how you are billed rather than only where post arrives. And it sets the dial code for the mobile number, because one-time sign-in codes are sent as texts and a number in the wrong country cannot receive them.
That phone number is worth keeping current for a second reason. It is the fallback when email is slow and the second factor when a super-user administrator signs in. An out-of-date number is a sign-in method you have lost without noticing.
What changes and what does not
Saving updates your account record. An invoice that has already been issued keeps the address it was issued with, because an invoice is a record of a document rather than a live view of your profile. Changing the address now does not rewrite last month's invoice and it does not need to.
New orders and new invoices use the address as it stands when they are raised, so the change takes effect from the next one.
Two things on your account cannot be changed from here, and it is worth knowing which. Your email address has its own card just below this one, because it is confirmed before it changes rather than edited in place, and the renewal date of a service follows the day it was ordered rather than being a setting. The renewal date is covered in how your renewal date works.
If you have changed country and expected your next order to bill the same way as the last one, check the currency shown at checkout before you pay. A moved account is the one case where the previous invoice is not a guide to the next one.