In the Account>Main information subtab:
Scroll to the logo section at the bottom of the page.
Browse for the image of your logo on your computer.
Ratio: original
Orientation: -
Max width: -
Max height: 120px
Max size: 3.5Mb
When the image shows in the preview, click Upload Logo.
When finished, click Save.
When your logo is uploaded, it shows in your online store, administrative documents, invoices, online registration confirmations and on your statements.