Upgrading Drupal

I have googled and searched this forum and cannot find step-by-step instructions how to update Drupal core from 7.0 to 7.2. I am hosting my site on godaddy.com, so I can access my server via the ftp client, but I do not know where or what I should be doing to make the update. I have found a way using myphp (come with godaddy hosting) to make a backup of my site. I am not a technical person but chose Drupal for my personal website for the challenge of learning something new, but I can't seem to get through this challenge.

My understanding is when upgrading contributed modules that you have to delete the module code from your web server before uploading the new code. But I am not sure whether you are meant to do this when upgrading core. For instance in Drupal for Dummies (p201) it just says "use a file manager or FTP program to copy the new files to your Drupal directory" - doesn't say to delete first. I guess this is because if I deleted the core code the site would disappear, right?

I just ran the 6.22 update from a 6.20 site. Unfortunately now I'm getting LOTS of persistent cron errors:

WD php: Unknown column 'bid' in 'where clause' [error]query: UPDATE blocks SET cache = 4 WHERE bid = 0 in /public_html/modules/block/block.module on line 280.

Any brilliant ideas what's going on and even better how to fix it?

Since upgrading last night, I am getting the following error on the modules list page:

Notice: Undefined index: distribution_name in drupal_install_profile_distribution_name() (line 202 of /home/cpelham/public_html/dev.crsny.org/public/includes/install.inc).

Just upgraded multisites from 6.0 to 6.22. Most of the sites show that the core files are 6.22, but several sites say that the core files need to be updated to 6.22. However, at the top of the status report it does show 6.22.

The issue appears only on the sites that use the aggregator module. When the aggregator module is deactivated the status report shows everything is up to date, but reactivating the module brings back the message that the core files need to be updated.

Tried running a cron, but the status report still shows that the core files need to be updated.

I build and release Drupal sites to owners, which I've built.

I maintain security and updates on these sites for owners after they are installed on their server.

The updating of modules is reasonably easy....

I'm curious why the Drupal core doesn't have a installer for upgrading quickly.

Currently, I disable all third party modules, reinstall a Garland Theme, backup the sites folder to my HDD. I then clear all cache.

I then remove all the folders/files from webserver that contain the recent Drupal core version.