Most WordPress themes allow you to set a custom header image which is displayed at an appropriate location in the theme, usually at the top.
Adding a custom header image
In case the theme supports a custom header image, you can upload it on your WordPress admin panel → Appearance → Header. You can also choose an existing image from your media library.
You can adjust the height and width of the header image after you have uploaded it.
Deleting custom header image
To delete one of your custom header images, you have to delete it in the media library. Please go to your WordPress admin panel → Media→ Library and click on ‘Delete Permanently’ below the image you want to delete.