This is the code for my next/old links. Yours may be different. This is in the "archives" template in the theme editor within wordpress:
Code:
<div class="navigation">
<div class="alignleft"><?php next_posts_link('<img class="alignnone size-full wp-image-3243" title="older-posts" src="CENSORED/wp-content/uploads/older-posts.jpg" alt="" width="248" height="74" />') ?></div>
<div class="alignright"><?php previous_posts_link('<img class="alignnone size-full wp-image-3243" title="newer-posts" src="CENSORED/wp-content/uploads/newer-posts.jpg" alt="" width="248" height="74" />') ?></div>
</div>
I made my own "Older posts" button using blank button graphics I downloaded from somewhere a long time ago. I would probably suggest not using images and find out how to use CSS buttons but either way works aesthetically.