How to change featured image and featured slider image size?

Hey Dude ! I really like your work. That a beautiful theme you made there. I’m using it on my website. But I face many issues. So I don’t know if you can help me.

1- I don’t know how I can add a custom logo at the header.
2- Is it possible to reduce slides dimensions?
3- Is it possible to reduce posts thumnails?
4- How can I move social buttons at the place of serach-bar and vice-versa?

Great and awesome work ! I hope to hear news from you soon !!

  1. There are option called “Header Options” inside Theme Options that allows you to change your logo
    2/3. For featured images, for both slider and posts, there are two values inside functions.php file
	add_image_size( 'slider', 1018, 460, true ); 		
	add_image_size( 'gallery', 474, 342, true ); 

Just change these values to ones you like
Afterwards you will have to regenerate these images since WordPress are not doing it automatically. Here is a great plugin that can help:
Additionally you can use this ( blog template which is already built-in theme. Just look for theme documentation for more info.
4. Unfortunately you will have to build your own solution for that.

Hope this helps.

And is it possible to add a small box just under each post, to présent a little bit who has wrote the post?

You can use one of many plugins that does just that. Here is one to give you an idea: