Magento upgrade through Magento connect

Following are the steps for upgrading from Magento 1.5.1.0 to this latest version of magento (Via Connect Manager):

1. Open Magento Connect Manager by navigating to System > Magento Connect > Magento Connect Manager.
2. After that fill your username and password used to access the admin panel.
3. Click check for upgrades in Magento Connect Manager  
4. As soon as the search for upgrades would finish, the “Upgrade to 1.5.1.0.1” will be listed for the Mage_All_Latest package in the Available column.
5. Select “Upgrade to 1.5.1.0.1” in the Actions column for the Mage_All_Latest package and click “Commit Changes”.
6. Package Mage_All_Latest Actions column, select “Last 1.5.1.0.1″ and click OK the changes.
7. Make sure whether the package upgrades installed successfully or not by viewing messages on the console.
8. Click the refresh button in the console window.
9. Go to the Settings at the top.
10. Select Beta in the Preferred State drop-down field.
11. “Save” the settings.
12. Click Back to the Extensions tab.
13. Click Check for Updates in the Manage Existing Extensions fieldset.
14. In the Actions column for Mage_All_Latest package, select “update 1.6.0.0-rc2 (Beta)” and click Commit Changes.
15. Ensure that the update package installed correctly by viewing messages on the console.
16. Click the refresh button in the console window.
17. Close MCM window and refresh the front end. The system is upgraded to Magento 1.6.0.0.
18. Magento Upgrade Error:

In case you receive “Service Temporarily Unavailable” page after refreshing your front end, then in that case you would have to open the Magento installation Directory on server and delete maintenance.flag file. After deleting this file go to Magento var directory, remove the cache directory and reindex all tables.

rm -rf var/cache var/session
chmod 550 ./mage
./mage mage-setup .
./mage config-set preferred_state stable
./mage list-installed
./mage list-upgrades
./mage install http://connect20.magentocommerce.com/community Mage_All_Latest –force
php shell/indexer.php reindexall