Hello Jean-Piere!
For that you want, you will need to modify a theme file, so I suggest you use the Agama Pro-Child theme to avoid the changes when the theme is updated.
Then follow the next steps:
1.Log-in to your hosting space (server) via FTP client.
On your server, find the agama-pro folder in the theme folder
(path should be this: … / wp-content / themes / agama-pro /)
2. find the agama-functions.php file inside the wp-content/themes/agama-pro/framework/ folder.
3. Copy that file to the wp-content/themes/agama-pro-child/framework/ folder.
4. Edit file in the agama-pro-child folder with some text editor (Notepad++)
5. search for words “ blog-large” in line 38.
6.Change the Width and Height value for the ‘blog-large’.
7. Save the file.
PS. You can also edit this file with the theme editor.
https://prnt.sc/iurysr
Regards