Manual Magento theme change
Automatic Magento theme installation done through Magento Connect Manager.
Here we go through manual installation steps.
1. Download a new theme and extract it. You will get app/ and skin
folders. Move content of the folders to magento_dir/app and magento_dir/skin folders.
2. Login to magento admin section. Navigate to System -> Design
3. Choose store, Click “Add New Design” and choose a new theme in Custom Design dropdown from a “default” branch.
4. Click Save. Navigate to Magento frontend in the browser and click refresh.