Resize slider for mobile version of website

Hi, I have a slider/promotional image set up for my website, which you can see under the menu bar HERE.

 

The link doesn't work in OP, so here it is: http://yourwebexample.co.uk/gymonline/

 

Your image link has a static width and height: <img width="900" height="203" src="http:/ /bla-bla.jpg" class="attachment-large">. Remove that width and height.

Then add this to attachment-large class:

.attachment-large {
width:100%;
max-width:900px;
height:auto;
}