change image size in media file selector of media module how can I change the size of the image that show in media file selector popup in media module
, I don't know which image style this module use, and how can I change the image style which is currently used or active.
The media module adds the image style 'square_crop' when it is enabled

you can alter this image style to change the display of thumbnails in the media browser (admin/config/media/image-styles/edit/square_thumbnail).

I believe the theme css also uses css to define the size, so to see the effect you will also need to make some changes in whichever theme is selected for the media browser (admin/config/media/browser):

.media-item img {
 border: 2px solid transparent;
 display: inline-block;
 margin-left: -2px;
 height: auto; /* override this in you theme */
 width: 100%; /* and this */
}