login via ssh and change to your Magento folder
Type the following two commands...
./pear mage-setup .
./pear upgrade-all
You may also have to reset permissions with the following three commands...
find . -type d -exec chmod 755 {} \;
find . -type f -exec chmod 644 {} \;
chmod +x pear
Lastly, clear your cache in your admin by going to your System menu, select Cache Management and then click 'Refresh all cache'.
That should be it but please check that any changes you've made to your theme are working with the new version. Often there's new features available in the updated default theme which may need to be carried through to your own theme. The release notes and changelog that comes with each Magento release often lists where changes need to be made.
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