1. How to Upgrade magento CE 1.7.X to 1.9.X
2. First step, take backup of DB and Magento 1.7.x files
4. Before you upgrade the pakage – check and note it down your Theme name and details. It will helpful to configure to new instance
3. Download Magento CE 1.9.x package and extract and install the fresh setup
4. After install 1.9.x – configure your 1.7.x database for latest instance. (or use default DB for testing later you can replace 1.7.x instance DB)
5. System > Tools > Compilation page and click on Disable
6. Once above steps is done,then clear cache and check your frontend and admin is loading with out error or not.
7. After successfull loading a page, then you have to copy following folders and files from 1.7.x and paste into 1.9.x package.
7.1 app/code/local
7.2 app/code/community
7.3 app/design/adminhtml (in case if you override admin then copy those files as well)
7.4 app/design/frontend/default/my-theme folder
7.5 skin/frontend/default/my-theme folder
7.6 skin/adminhtml/default/my-admin-style (in case if you add/edit/change admin style related files)
7.7 root/scripts/ (in case if have any script files from your 1.7.x instance)
7.8 Media and JS folder, In case any custom files you have in you existing instance, then replace to new as well
8. Clear Cache
9. Do re-index once
10. Check your frontend and admin. 1.9.x changes will reflect.
