Hi Mustafa,

Thank you for writing in.

To clarify, are you referring to the post grid items in your homepage?

Alternatively, if you're referring to the nectar slider, here's an article and a video that can help with this.
https://themenectar.com/docs/salient/nectar-slider-plugin/
https://www.youtube.com/watch?v=FLU9Pxo_RD8

Try that and let us know how it goes, we look forward to your reply.

Cheers,

Hey Again,

The Images can be changed by adjusting the "Featured Image" Metabox of that particular Portfolio or Blog Post Item that is selected to be shown in the "Post Loop Builder" Page Element. 

Best,