The contact information on the out of the box Contact Us page is fed directly from your company profile. In order to update this you must have admin permissions.
When logged into the Control Panel, follow these steps:
Click on your company name and a menu of options will be displayed.
Select Company Profile
Make the necessary changes to your contact information. Keep in mind this company information is shared throughout all of your generated pages.
Upon saving the system will now leverage this contact info for new requests.
Please note that your web site caches the company information for 60 minutes. So you may not see the change reflect immediately. If you would like to see it immediately, simply clear your cookies or browse in Private mode.