Customising Invoice

In order to populate information under the ‘From’ section of the invoice do I need to customise the php file or can it be done from within the backend of the shop theme?

In Hussain’s first post on this topic it was mentioned “I know how to change what goes into no. 1 from the invoice settings.”

However I am unable to find invoice settings also do you know how to customise the invoice number? I am getting a really ugly looking long invoice number such as:

Invoice #5ac3d7def089d554b63b88b39e971b88

I would appreciate it if anyone can point me in the right direction.