Pretty simple.
Open up rsgallery2.php and goto around line 300.

Fine the following code:

and replace 5 with whatever you want as the default value.

Good luck

Hello, in my page: http://uag.awardspace.com/index.php?option=com_rsgallery2&Itemid=30

In version 1.12.1, I obtained it of the following way:

1) Open up rsgallery2.html.php (not rsgallery2.php)
2) goto around line 848    or    find=> function RSGalleryList

    function RSGalleryList( $gallery ){
        global $Itemid;
       
        $limit = mosGetParam ( $_REQUEST, 'limit', 5);
        $limitstart = mosGetParam ( $_REQUEST, 'limitstart', 0);

3) and replace 5 with whatever you want as the default value.

Good luck
Atte: Pedro Alejandro González Oceguera, from Mexico.