Hi zmand13
You can add to your custom.css file this code
.acm-slideshow .owl-carousel .item .mask {
background:transparent!important;
opacity:0.9!important;
}
The background code remove completely the mask
if you indeed want to control only the opacity then do not add the background code and change opacity value.
If you do not have already a custom.css file then create it in this folder /templates/ja_alumni/css/
Regards