To edit your RSS button, go to Layout-Edit HTML.
Find following codes :
<div class='rss'>
<a href='http://grungeblogtemplates.blogspot.com/feeds/posts/default' target='_blank'><img src='http://i44.tinypic.com/34te8ow.png'/> Post </a> <a href='http://grungeblogtemplates.blogspot.com/feeds/comments/default' target='_blank'><img src='http://i44.tinypic.com/34te8ow.png'/> Comments </a>
</div>
Change http://grungeblogtemplates.blogspot.com with your blog url.