1. Login to your WordPress admin panel http://www.yoursite.com/wp-admin/ or where you have installed wordpress, for example in subfolder – http://www.yoursite.com/subfolder/wp-admin/.
2. After login go to Appearance in the left side bar of WordPress than click on themes.
3. In theme panel to change theme click on Add New Theme box or click on Add New button appear on top of the panel.
Add New Button :
Add New Theme Box :
4. After click on add new, it will show you best free themes available on WordPress market. Click on Featured, Popular or Latest to see all available free themes.
5. Choose best theme that you like or suitable for your website. Click on it, it will show you preview with install button. Click on Install button to install theme.
6. After installation, you need to activate theme first to make this working on your website. So click on Activate link, it will show you just after installation.
7. After activate click on Visit Site link, or open new window and type your website URL where you have installed WordPress.