So I've search during some hours how to change image size in existing post. I know that wordpress create many image with different size (acording to my theme) for each uploaded image. But he didn't create it for old image that was existing and used before the theme change. So old image didn't have many size. I've used Regenerate thumbnails to recreate it. So far so good.
New post automatically display size options when uploading new image before inserting in the post. But old post didn't have changed (automatically) the image url to the large size, they still have the original size. And there are no options when opening image (by double clicking on it in the post) to change the image url/size.
Do you know a way to have the same option to choose the image size when editing and not only inserting ? or anything ?
There is a way to select the desired image url and edit the source url for each image but it's quiet long...