How to install themes and plug-ins under Wordpress?
From the Wordpress dashboard, go to Appearance > Theme.
Select "Free Wordpress themes" and click on "Add New".There are many web developers who contribute to the Wordpress community by creating new innovative theme and are generous enough to post them for free
You will be presented with a list of themes based on their rating (highest first).You could either preview the theme on your blog or install them directly.
Its recommended you have at least 2-3 articles on your blog (with pictures) to have an exact idea of how the theme will look like!