wait… i can’t recognize, are you using the minimatica gallery view or those from wordpress itself?
in second case everything i wrote in the post before is right.
in the first case you have to change #container width to 1200 in style.css then in function.php straight above the line:
// If 3 images have been shown, end the image row and open a new one
there is a line :
<?php if( !( $counter % 3 ) && ( $attachment != end( $attachments ) ) ) :
you have to change 3 with 5 there