Problem using plugin

Hi, this is exactly what i need, the problem is being old ,inexperienced and a numpty I cannot work out how to use it correctly.
I have copied a shortcode (I think) into my page here
http://www.ncirossallpoint.co.uk/camera/
But have no idea how to make the image smaller,the refresh rate is perfect if you could help it would be greatly appreciated.

Thanks

https://wordpress.org/plugins/image-autorefresh-shortcode/