when images are uploaded, they are resized based on the settings in the admin/common/properties.php file.
there are two types of images settings, proportional an cropped. the sizes for these are set in the following arrays:
$GLOBALS['resize_proportional'] = array(
array('w' => 1024, 'h' => 768, 'watermark' => true),
array('w' => 782, 'h' => 481, 'watermark' => true),
array('w' => 163, 'h' => 92)
);
$GLOBALS['resize_cropped'] = array(
array('w' => 62, 'h' => 62),
array('w' => 132, 'h' => 140),
array('w' => 102, 'h' => 102),
array('w' => 42, 'h' => 42),
array('w' => 782, 'h' => 481, 'watermark' => true),
array('w' => 999, 'h' => 260, 'watermark' => true)
);
if you wish to use a different image size, you will need to add it to these arrays, then re import your images.