How to alter showtime gallery slideshow images

Hi Liesbeth,

The dimensions you set in the options have to do with the actual image dimensions, not the display dimensions.
The display dimensions are controlled by CSS. For example you may have an image sized at 300 pixels width and displayed in 600 pixels or 100 pixels in your page.

Now, to the actual question. You are using the slideshow layout in the example page you provided. This layout has some options to help you define the number of thumbnails you wish to display depending on the screen viewport.
So for your case make sure to set the options named "Items to show" and "Items to scroll" to 1 for smaller screens. Make sure to adjust accordingly for different screen sizes using the section named "Responsive Options".
Those options can be found under the "Display" tab of the gallery.

Please let me know if you need more help with this.

Regards