Add in your local config, changing the values you want

// +-----------------------------------------------------------------------+
// |                                upload                                 |
// +-----------------------------------------------------------------------+

// upload_maxfilesize: maximum filesize for the uploaded pictures. In
// kilobytes.
$conf['upload_maxfilesize'] = 200;

// upload_maxheight: maximum height authorized for the uploaded images. In
// pixels.
$conf['upload_maxheight'] = 800;

// upload_maxwidth: maximum width authorized for the uploaded images. In
// pixels.
$conf['upload_maxwidth'] = 800;

// upload_maxheight_thumbnail: maximum height authorized for the uploaded
// thumbnails
$conf['upload_maxheight_thumbnail'] = 128;

// upload_maxwidth_thumbnail: maximum width authorized for the uploaded
// thumbnails
$conf['upload_maxwidth_thumbnail'] = 128;

Administration -> Plugins -> LocalFiles Editor

add lines then you modifie

Thnxs

It's solved