thumbnail cropping?

How can I stop the thumbnail from cropping through the middle (especially in featured image) I want that to be the full image just resized.
I tried these instructions and only succeeded in making the crop include the top
Step2. Find the function named “image_resize_dimensions” (Around line 309). Unfortunately this function is not pluggable and doesn’t use any hooks so we will edit it directly. Find the lines:
1 $s_x = floor( ($orig_w – $crop_w) / 2 );
2 $s_y = floor( ($orig_h – $crop_h) / 2 );

change to:

1 $s_y = 0; //floor( ($orig_h – $crop_h) / 2 );

What would I do to get the bottom to show?
thanks!
Heather