Next/Previous button for nodes within a book
ok, this can be achieved by overriding of modules\books\book-navigation.tpl file. Copy this file to your Theme and change following:

 &lt;?php if ($has_links): ?&gt;
    &lt;div class="page-links clearfix"&gt;
      &lt;?php if ($prev_url): ?&gt;
        &lt;a href="&lt;?php print $prev_url; ?&gt;" class="page-previous" title="&lt;?php print t('Go to previous page'); ?&gt;"&gt;&lt;?php print t('‹ ') . $prev_title; ?&gt;&lt;/a&gt;
      &lt;?php endif; ?&gt;
      &lt;?php if ($parent_url): ?&gt;
        &lt;a href="&lt;?php print $parent_url; ?&gt;" class="page-up" title="&lt;?php print t('Go to parent page'); ?&gt;"&gt;&lt;?php print t('up'); ?&gt;&lt;/a&gt;
      &lt;?php endif; ?&gt;
      &lt;?php if ($next_url): ?&gt;
        &lt;a href="&lt;?php print $next_url; ?&gt;" class="page-next" title="&lt;?php print t('Go to next page'); ?&gt;"&gt;&lt;?php print $next_title . t(' ›'); ?&gt;&lt;/a&gt;
      &lt;?php endif; ?&gt;
    &lt;/div&gt;
    &lt;?php endif; ?&gt;


to:

&lt;?php if ($has_links): ?&gt;
    &lt;div class="page-links clearfix"&gt;
      &lt;?php if ($prev_url): ?&gt;
        &lt;a href="&lt;?php print $prev_url; ?&gt;" class="page-previous" title="&lt;?php print t('Go to previous page'); ?&gt;"&gt;&lt;?php print t('Back') ?&gt;&lt;/a&gt;
      &lt;?php endif; ?&gt;
      &lt;?php if ($parent_url): ?&gt;
        &lt;a href="&lt;?php print $parent_url; ?&gt;" class="page-up" title="&lt;?php print t('Go to parent page'); ?&gt;"&gt;&lt;?php print t('up'); ?&gt;&lt;/a&gt;
      &lt;?php endif; ?&gt;
      &lt;?php if ($next_url): ?&gt;
        &lt;a href="&lt;?php print $next_url; ?&gt;" class="page-next" title="&lt;?php print t('Go to next page'); ?&gt;"&gt;&lt;?php print t('Next'); ?&gt;&lt;/a&gt;
      &lt;?php endif; ?&gt;
    &lt;/div&gt;
    &lt;?php endif; ?&gt;