Remove Thumbnails From Posts

Hello:

I’ve seen this topic before but I’m not sure if the same instructions apply to my theme:
https://fthemes.com/demo/Douched/

I need to use the featured image option for the slider but I hate the thumbnails that come with every post. I am not a code person but I can follow instructions. This is my site: https://www.kickmag.net/

and any help is appreciated.

Thank You,
Tamara