I'm using the "Featured Image" in the admin post page and I'd like to choose the size of the image. http://screencast.com/t/4c5rUGcOX
Actually my theme is set up to show up that image with a fixed size :
<a href="<?php the_permalink() ?>" rel="bookmark"><?php the_post_thumbnail('home-thumbnail', array('class' => 'alignleft')); ?></a>
How can I make it flexible so I can choose each time the size I prefer?