How do I add images to slider and remove the default images permanently

I just downloaded the Planshet theme. I can't for the life of me figure out this slider. Every time I try to add a custom image and delete the default images they just reappear again once I visit my site and my custom image doesn't appear.

What do I do to fix this problem?

It's like I can't make any changes to the slider.

Hi!
Do you save changes by clicking a check mark on the right after adjusting your slider?