changing image of the header

Hello Kris,
You can't have different header for every post. What you can do is:
1) have different header for Home page
2) Create several Post templates and add different banner not to the header area but under it, where it says Post Template here:

Gina
Themler Support

Hello i don't think this can work. The articles are located in a blog page. When, i click on the read more button i want to have a new slider. So i think they use the page template. I maked different page templates but i can't link them to a article. See for your selves test-ararin.be/test1 > verzekeren > articlke read more

Hello,

In Joomla theme the Post Template or the Page template is used for a Joomla Single Article Layout because there are no separate Post and Page content types in Joomla. The difference is that Post Template contains article article metadata like Author, Published Date, Hits, Category, etc. Once metadata is disabled for the article from Joomla back-end, the article will have Page Template styling. If at least one article metadata icon is enabled, the article will use Post Template.

Sincerely,
Nettie

how do i link a different post template to an article : article 1 > post 1 ... article2 >post 2

Kris, I apologize, I had an impression that you were using Wordpress, it is possible to assign different post template to each article (even in wp-admin).
But for Joomla, the option is not available you would need to add slider as part of the article content.

Gina
Themler Support

i solved it by making a invisible menu and link the articles to that menu, so i can add a page template