chm on "zpBase: Problem with image size"

Hello,
I just built my web site with zenphoto using zpbase theme. I'd like to ask you something because I have a small problem.
In my administration page>option>theme>standard options, I see that the image size is set to 960 then there's four options : height, width, smaller side, largest side.
I can't change the size and none of these 5 options.
I'd like to be able to change it because I have vertical pics that are to high and people need to scroll down to see the bottom of it.
Thank you for your help.
Christian