Lost header AND Logo no show in Facebook updates

I am having difficulty with my website images and info showing up when i do a facebook post which includes my web address. What i would like to happen is when i do a post and put in my url i want my logo to come up and some information about my site.

What currently happens is i get some random images to choose and some of the text from my front page.

Ive had a look through some questions about how to get what i want and it says i must do some stuff within the header. Unfortunately i don’t have access to the editor anymore. I installed a security plugin after being hacked and it makes the editor disappear. So i have no idea how to get to the header anymore and if i do manage to find it i don’t know what to do when i get there.

If anyone is able to help can you put your answers in as plain a language as possible. Imagine you’re explaining to a 7 year old. I do find some of the help as confusing as the problem.

Oh yes if it helps in any way I’m using the Customizr theme.

Thanks a million in advance