You can replace the header image from Appearance > Customize > Header Options > Header Image and you can also get the options to hide the search options there.
The link you given above is not using our theme. Please check and verify once.
If so, you can check the Feature Page options from Appearance > customize > Featured Section Options and select the page for the slider section. If you select the parent page, its child pages will be the slider items. Kindly check this link for more help.