How to show images uncropped after uploading?

The theme you are using crops uploaded pictures, but there is always a version of the picture which keeps the original full size. Modify the code that render the picture that it will use the size parameter.

Use: wp_get_attachment_image:
echo wp_get_attachment_image( $attachment->ID, 'full' );
Or: display post_thumbnail:
echo get_the_post_thumbnail( $post->ID, 'full' );

'full' here means the full size