Go to Settings cog > Company Profile > Logo & Color.
Your account can only have one logo on all CRM content (Quotes, Invoices, Purchases, Automated communication) you could have a combined image of multiple logos if you have more than one business working together.
All company information is pulling from one location in your Company Profile. If you would like to have an alternate header on your forms this is possible through our Professional Services Team. To discuss this further you can book in a call here or email [email protected].