How can I set the Carousel/Showcase slider to show more slides?

You can learn more about the difference between the two slider type's behavior here.

Carousel

The amount of slides this slider type displays depends on the set slider size, slide size, minimum slide distance and maximum pane width.

Example:

Set slider size 1200x500px 1200x500px 1200x500px
Slide size 400x400px 400x400px 250x400px
Minimum slide distance 0px 20px 10px
Maximum pane width 3000px 3000px 1200px
Browser width 1200px 1200px 1200px
Displayed slides 3 2 4

Basically, if you would like your slider to show more slides, you should increase the slider size, or reduce the slide size, slide distance or maximum pane width.

Showcase

The amount of slides this slider type displays depends on the set slider size, slide size, slide distance. The visible slides might make a difference as well.

Set slider size 1200x500px 1200x500px 1200x500px
Slide size 400x400px 250x400px 250x400px
Slide distance 60px 10px 10px
Visible slides 3 3 10
Browser width 1200px 1200px 1200px
Displayed slides 1 full, 2 partial 4 full, 1 partial 5 full, 2 partial

Basically, if you would like your slider to show more slides, you should increase the slider size or the visible slides, or reduce the slide size, or slide distance.