Click Clients to the left of the page, once the list has loaded you'll see that your client's name is underlined in blue text, click their name to open their client file.

At the top of this page, you can press the pencil icon to change the client's address details.

If you need to adjust your contact's details then you will need to press the pencil icon in line with the contact that needs changing.

Near the top of this page you can click Client Variables, Services or Proposal/LoE to view and edit these details.