How to resize the flexslider?

I’m using the following template to build my school website.
https://themes.quitenicestuff.com/parkcollegewp/

They have used the flex slider in their template.But instead of a full size slider I need the size of the slider to be reduced to my header size.

Here is the flexslider.css

/* Browser Resets */
.flex-container a:active,
.slider a:active,
.flex-container a:focus,
.slider a:focus  {outline: none;}
.slides,
.flex-control-nav,
.flex-direction-nav {margin: 0; padding: 0; list-style: none;} 

/* FlexSlider Necessary Styles
*********************************/
.slider, .slider-blocks, .page-slider {padding: 0;}
.slider .slides > li, .slider-blocks .slides > li, .page-slider .slides > li {display: none; -webkit-backface-visibility: hidden;} /* Hide the slides before the JS is loaded. Avoids image jumping */
.slider .slides img, .page-slider .slides img {width: 100%; display: block;}
.flex-pauseplay span {text-transform: capitalize;}

/* Clearfix for the .slides element */
.slides:after {content: "."; display: block; clear: both; visibility: hidden; line-height: 0; height: 0;}
html[xmlns] .slides {display: block;}
* html .slides {height: 1%;}

/* No JavaScript Fallback */
/* If you are not using another script, such as Modernizr, make sure you
 * include js that eliminates this class on page load */
.no-js .slides > li:first-child {display: block;}

/* FlexSlider Default Theme
*********************************/
.slider, .slider-blocks, .page-slider { background: transparent; position: relative; zoom: 1;}
.flex-viewport {max-height: 2000px; -webkit-transition: all 1s ease; -moz-transition: all 1s ease; transition: all 1s ease;}
.slider .slides, .slider-blocks, .page-slider {zoom: 1;}
.carousel li {margin-right: 5px}

/* Direction Nav */
.flex-direction-nav {*height: 0;}
.flex-direction-nav .flex-disabled {opacity: .3!important; filter:alpha(opacity=30); cursor: default;}

/* Control Nav */
.flex-control-nav {width: 100%; text-align: center;}
.flex-control-nav li {margin: 0 3px; display: inline-block; zoom: 1; *display: inline;}
.flex-control-paging li a {width: 11px; height: 11px; display: block; background: #666; background: rgba(0,0,0,0.5); cursor: pointer; text-indent: -9999px; -webkit-border-radius: 20px; -moz-border-radius: 20px; -o-border-radius: 20px; border-radius: 20px; box-shadow: inset 0 0 3px rgba(0,0,0,0.3);}
.flex-control-paging li a:hover { background: #333; background: rgba(0,0,0,0.7); }
.flex-control-paging li a.flex-active { background: #000; background: rgba(0,0,0,0.9); cursor: default; }

.flex-control-thumbs {margin: 5px 0 0; position: static; overflow: hidden;}
.flex-control-thumbs li {width: 25%; float: left; margin: 0;}
.flex-control-thumbs img {width: 100%; display: block; opacity: .7; cursor: pointer;}
.flex-control-thumbs img:hover {opacity: 1;}
.flex-control-thumbs .flex-active {opacity: 1; cursor: default;}

Even though I changed the width from 100% to 1000px it doesn’t change.What should I do?Please help me.
Thank you