Two easy ways to add a header image:
In your dashboard, got to Appearance + Header and just add it there. You can also add/delete a header image under Appearance + Customize (which will bring up a new sidebar menu of other options you can change.) From there select “Header Image.”
Really do love your template — I chose to upgrade it because I was impressed by the responsiveness. Glad to see which php to comment out — I too really hated the forced featured image at the top of things.
Keep up to good work — your customer support is impressive.