反向显示博客条目和评论，Ruby on Rails

I am new to rails so could use some help here. I have followed several tutorials to create a blog with comments and even some of the AJAX bells and whistles and I am stuck on something that I hope is easy. The default display for both blogs and comments is to list the oldest first. How do I reverse that to show the most recent entries and the most recent comments at the top. Don't really know if this is a function of the controller or model. I have done some customization so here is the code for the controller .rb files if it helps. I am new to rails so could use some help here.