Saving changes in wp_editor

First of all the the_editor() function has been deprecated and it’s advised to use the wp_editor() instead.

Just to explain how the value is being saved, your value in the textarea isn’t being saved by the textarea element but instead and most likely by update_post_meta.

To replace your textarea with wp_editor, you can define it as below:

$content   = stripslashes( $rowimages->description );
$editor_id = "im_description" . $rowimages->id;

wp_editor( esc_html( $rowimages->description ), $editor_id );