You can adjust Easy Digital Downloads archive columns using the conversions_edd_archive_classes hook. Below is a code example to accomplish this. Just replace the edd_download_columns_2 selector inside the $replacement variable to whatever you desire.
Code Example
/**
* Change Easy Digital Downloads archive columns.
*
* @param string $classes Archive column classes.
*/
add_filter('conversions_edd_archive_classes', 'conversions_edd_archive_add_class');
function conversions_edd_archive_add_class( $classes ) {
// Add the 2 column downloads grid class instead
$replacement = array( 1 => "edd_download_columns_2" );
// Replace the default class in array
$classes = array_replace( $classes, $replacement ); return $classes;
}