Hi,
To change the arrow position, add this on your custom.css
.numeric_controls, .arrow_controls {
position: absolute;
bottom: 10px;
}
You can change the thumbnail size on functions.php, find this code
$avia_config['imgSize']['fullsize'] = array('width'=>930, 'height'=>930, 'crop'=>false); // big images for lightbox and portfolio single entries
$avia_config['imgSize']['featured'] = array('width'=>1500, 'height'=>430 ); // images for fullsize pages and fullsize slider
$avia_config['imgSize']['featured_small'] = array('width'=>990, 'height'=>280 ); // images for fullsize pages and fullsize slider
$avia_config['imgSize']['portfolio'] = array('width'=>495, 'height'=>400 ); // images for portfolio entries (2,3 column)
$avia_config['imgSize']['portfolio_small'] = array('width'=>241, 'height'=>179 ); // images for portfolio 4 columns
Those are the thumbnail size, please refer to the description note.
Regards,
Ismael