But i want that the standard size of the picture is width (400px) height (300px)

Do you want all uploaded images to be resized to these dimensions, or are you referring to setting the size of existing images?

Happy that you found a solution, and there are a few other options: 1. In Editor Profiles -> Editor Parameters -> Filesystem, set Upload Reisze Options to No, Upload Resize State to Yes, and in the Resize area, set the Width and Height value for resizing. All images the user uploads will be resize to fit within 400 x 300. 2. Use the max-width and max-height css styles as above, but added to your template stylesheet, with a special css rule, eg:

img.max_size {
    max-width: 400px;
    max-height: 300px;
}

then in the Image Manager Extended parameters, set a Classes value of max_size, which will be added to every image inserted. You can then adjust the max-width and max-height values in future, to affect all images with the class value.