You can achieve what you want with some CSS, but without a link to your site it's not possible to give an exact answer.
Using your browsers "Inspect" tool, locate the correct element. The title is probably a <h3> tag, but you'll want to add a class or ID in order to change the slideshow title only.
I've used the following code previously to edit the title of Image Show GK4, but you might have to modify it to fit your template:
.gkIsWrapper-gk_shop_and_buy .figcaption h3 {
// Your CSS styles here
}
Add this to your CSS file. You might have to add !important to the CSS styles to make sure they are applied.
Hope this helps.