Magento Upgrade from 1.7 to 1.9

Upgrade Roadmap for CE 1.9.0.1 from 1.7

1. Take a backup of current database and current 1.7 code. place maintenance.flag file inside 1.7 code folder to put website offline.
2. Download latest magento from the http://www.magentocommerce.com/download
3. Remove all folders and files from your 1.7 code except maintenance.flag (but you should have backup somewhere) and place all folders and files from the 1.9.
4. Now from your 1.7 merge your following custom folders into the 1.9
   • Community app/code/community
   • Local app/code/local
   • Media
   • your theme or package (app/design/frontend/default/<your theme> or app/design/frontend/<your package>)
   • custom folders from Skin (both for adminhtml and frontend).
   • copy your custom xml files from app/etc/modules/ to current app/etc/modules/
   • any custom admin theme folder from adminhtml/default/yourtheme.
   • copy your custom folders from adminhtml/default/default/ (1.7) to adminhtml/default/default/ (1.9).
   • custom js files if any from app/js/.
5. Now go to app/etc/local.xml.Edit database details their.put your database username and password and database name.
6. Remove maintenance.flag file and check the site in the browser. it is done.