Thank you Andrew for sharing this.

Ciarán

Some year ago there was the Header Tag plugin which did this easly.
Now Header tag plugin is not in JED and its web site is closed.
I found another free plugin that changes from h2 to h1. I tried it and it seems to work.

Aimy H1 Heading: https://www.aimy-extensions.com/joomla/h1-heading.html

Among the free extensions you'll find also Aimy No Generator: https://www.aimy-extensions.com/joomla/no-generator.html
that delets "generator" meta tag from the HTML code.

I hope these information may be usefull to someone.
Thanks
A nice day
Andrew

Thank you! Finally I asked a Joomla specialist in the Netherlands to fix it for me.

Hello

If you wish you can use the template to override your Joomla output by creating overrides. Navigate to Extensions -> Templates -> Templates -> [YourTemplate] -> Create Overrides. Select the component you wish to override (most likely com_content). Once created navigate to the html folder within your template. Navigate to the component override you just created. From here you will see each view for the component. Each view can be edited to your own taste (replace H2 with H1).

Ciarán

Yes I know, but most titles of the articles are h2 tags. For seo reasons, I want to change those H2 tags in H1 tags, but with the same font and size (no bold) the h2 tags have.

Hello

The only H1 heading on this page is the 'Recente berichten' which text which appears to be already in bold.

Ciarán

http://Www.carolinedereusfotografie.nl

Hello

Would you have a URL to an example of your heading? In most cases you can add the following to the Custom CSS field of your templates parameters to set the font-weight...

h1 {

    font-weight: normal;

} 

Ciarán

Hi, thank you for your answer! I installed the plug-in, but it doesn't work. I am getting an error (500). Now I tried to change the html code manualy, but then I am getting a wrong bold font.

Hello

For better control of your headings may I suggest the following extension.. https://extensions.joomla.org/extension/header-tags/

Ciarán