To make sure your new address is consistent throughout the App, you will need to update it in two places.
Firstly, update your address in the web based app under Settings>Business Information to make sure the app has your address correct.
Secondly, you will then need to update your letterhead so your outgoing documents are correct by navigating to Settings>Other Settings>Letterhead. Please note that this change will only apply to documents you generate after the change is made, to create retroactive documents you will need to recreate the PDF stored in the system by clicking on 'view draft' from withing the session or invoice on the web based app.