Hi @gophumek, I think you probably changed line of code in
archive.php that looked like this:
$image_img_tag = wp_get_attachment_image( $image->ID, array(100, 85) );
where you changed
There are actually 3 of these that you need to change.. The first one is in line#44 and the code is like in the above.
The second one is within line# 53 and looks like this:
?php the_post_thumbnail( array(100, 85) ); ?>
and the third one is in line #60 and looks like this:
$my_image = wp_get_attachment_image( $firstimg->ID, array(100, 85) );
if you notice all of these have
85 which correspond to width and height respectively.
One other thing. If you are doing any modifications to a theme, I highly suggest creating a child theme and doing your modifications from there.
Here is a good article from WPTuts Plus http://wp.tutsplus.com/tutorials/theme-development/child-themes-basics-and-creating-child-themes-in-wordpress/
while here is the official article from WordPress Codex: