Assuming you use semantic template, open up the file <yourinstall>/components/com_rsgallery2/templates/semantic/html/gallery.php.
There you will find a code block, like this:
<?php
if($this->gallery->id == 0){
// show random and latest only in the top gallery
//Show block with random images
$this->showImages("random", 3);
//Show block with latest images
$this->showImages("latest", 3);
}
if( $this->pageNav ):
?>
Move this anywhere in the template to modify the page layout.
Smart thing todo here is create a copy of the semantic template, and modify this copy to your liking.
This way you can bakcup just that template when upgrading and upload it once the upgrade is complete.
Good luck!