downloading updates

As a novice, having probs w/upgrading. I tried to follow directions, and do not understand definitions to most of the terminology. I am using yahoo webhosting w/wordpress 2.3.3 version. I hit the download 2.5.1 key, got a new window w/zipped files. extracted files (I assume this is what is meant by “upload”?) then got stuck.

I think I am supposed to find /wp-admin/upgrade.php, but cannot find it.

I also tried to download the wpac, but do not know how to use it or if it is properly installed.

my goal is to connect to more themes and thought i needed to update to do this. please help.

thanks