Comment on WordPress Header Images by SEO Dave.
They go under your themes folder
With the filename as described in the tutorial above.
If you do multiple sets of banners use
For your second set and 03 for the third and so on.
You don’t have to use FTP, if your control panel allows you to upload images to the above folders you can use the CPanel.
Make sure you use the filename formats described in the tutorials,
Banners are: landscape-1.jpg, landscape-2.jpg etc…
Headers are: c1.jpg, c2.jpg or c1.gif, c2.gif