Login to your dashboard and just go to Appearance > Customize > Design Options > Custom CSS and paste below custom CSS code to reduce the white space between ‘Homepage Slider’ and ‘Text’ below.
#main {
padding-top: 10px;
}
@media only screen and (max-width: 767px){
#main {
padding-top: 10px;
}
}
It seems that you have set the fixed height to all the devices via Revolution slider settings. Just see this tutorial video to set the different height for different devices.