adding attached images to theme at certain size

i created a new (very basic) mobile theme for my site. i have found out how to show all the images attached to the post but they are all 90×90 thumbnails. i cant figure out how to change the size of the thumbnails though. I can make the image bigger but it gets distorted. I would just like to resize the images that appear. can someone point me in the right direction? im using this code to show the attached images:

<?php echo show_all_thumbs(); ?>