It is very easy to upgrade wordpress, just upload and replace the files in your wordpress directory with the newer files, every file has a modification or creation date, it is usually easy visible in an ftp client, after you've done, just use the upgrade.php file and thats all, if your configuration file has all the details of database name, user and password, it will use the same DB and you'll be using newer WP version..
The main problem with upgrading is: don't delete all the files and upload new files, you don't have to do that, because you need the config file and besides, some files are modified by your needs if you have added a new template or edited something yourself, if you didn't and are using the default, then only config file is needed..
I wish wordpress would again would be releasing upgrade packages, with only changed/edited files from the last release, but maybe it is only a waste of time though.
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