The information within your 'Company details' section is used in your communications with your customers and work addresses. If you make your letterheads using the Commusoft tool (not using your own full letterhead and footer images) these details will be used here too. These details can be edited at any time.
In order to edit your company details, first, open your company settings. The first setting under 'General settings' will be your 'Company details'. The required fields here are marked with an asterisk. Once you've made your changes, click 'Save'.