2) Download the latest magento package
wget http://www.magentocommerce.com/downloads/assets/1.6.0.0/magento-1.6.0.0.tar.gz
tar xvfz magento-1.6.0.0.tar.gz

3) Go to the terminal and change the directory to the location where the current magento site is running
4) Remove all the cache files $ rm -rf var/cache/*
5) Remov the folder downloader $ rm -rf downloader
6) Copy the folder “downloader” from the latest package to the current site $ cp -a magento/downloader
7) Move the file “ mage” from the latest package to teh current site  $ cp magento/mage
8) Chnage the permision $ chmod 550 ./mage
9) Run the following commands

$ ./mage mage-setup .
$ ./mage sync –force
$ ./mage install http://connect20.magentocommerce.com/community Mage_All_Latest –force
$ rm -rf var/cache/* var/session/*
$ rm -rf downloader/pearlib/cache/* downloader/pearlib/download/*
$ chmod 755 mage
$ php shell/indexer.php reindexall
$ ./mage upgrade-all –force

10) Copy all the file from latest package to the current site except the theme folder that the current site use
$ cp -Rf magento/* .

11) point the browser to the site url

This may take more time . so be patient. You might  get a browser error when the upgrade is being done . never mind 🙂 It normal .

12)  Thats all !!!