Hello,
You can decrease the slider size at the bottom. Add the following code into custom.css file:
.slider-container { height: 500px; }
To create custom.css you can rename default.custom.css to custom.css.
Make sure you enabled this file in Theme Options > Custom CSS > On.
Please provide us with the admin panel credentials to check the header issue.
Have you made any changes to the original theme files?
Regards,
Eva Kemp.