Help my Parallax to work please!

Hi everyone,

I have the parallax feature working on my website which is running on the Gridstock theme, BUT the height of the viewable area when you scroll is much too shallow compared to the large viewable area on the demo site. I have looked on the support forum (which is no longer updated which I didn’t know about when I purchased the theme!) and there are no answers.

If anyone knows how to alter the height of the viewable area for the parallax themewich shortcode feature in the Gridstock Theme PLEASE reply and put me put of my misery!

I think I found the corresponding css file that refers to the parallax image (see below), as it stands the height is always 175px when I view it online even though in the css it says 100%, but I’ve changed the height from 100% to 500px for example and nothing happens:

.tw-post-break .tw-opacity {
position: absolute;
top: 0;
left: 0;
width: 100%;
height: 100%;
z-index: 2;

All and any help will be much appreciated.
Thank you in advance.

or it could be this, but again no mention of height:

.tw-post-break .tw-parallax-content {
position: relative;
z-index: 3;