how to delete the search bar from the header,

Go to style.css and look for:

#header #searchform {
float:right;
margin:32px 3.4% 0 3px;
}

then, include the line display: none; inside of this, like that:

#header #searchform {
float:right;
margin:32px 3.4% 0 3px;
display: none;
}

Enjoy!