Change image size of Slider Images

I would like to make the images that show in the slider wider to be 725px in width instead of 600. I have changed the width in the stylesheet as follows:

.kwicks .post {
position:relative;
padding:0;
width:725px;
height:400px;
border: #F9F9F9 7px solid;
}

.opacity {
display:block;
position:absolute;
top:0;
left:0;
z-index:1;
width:725px;
height:400px;
background:#F9F9F9;
opacity:0.1;
}

.overlay {
display:block;
position:absolute;
top:0;
left:0;
z-index:1;
width:725px;
height:400px;
}

In functions.php on line 59 I have also changed:
add_image_size( ‘slider-thumb’, 725, 400, 1 );

to reflect this.

However, even though the container of the slider images has resized to 725px, the actual photos inside still come out as 600px wide, even though I have re-uploaded them in 725px wide.

Can somebody tell me please what I am missing? I have also checked under “media” in “settings” in the WP dashboard, but I don′t think it has anything to do with it…

Please help? Thanks.

Website is: https://www.casalefranco.com