Can I upgrade my operating system by myself?
There is an important distinction between ‘update’ and ’upgrade’.
An update contains bug fixes, new drivers and minor software improvements and is usually available as a free download. This is also called a ‘patch’, because an update is made of software that is already present.
An upgrade, on the other hand, is a more fully featured version. For example, when you buy a new version of the software you are currently using. This usually involves an upgrade cost.
You can perfectly perform software updates yourself on your system (if ‘unmanaged’ servers). A software upgrade, on the other hand, you are still not allowed to perform by yourself. For instance, you are not allowed to upgrade Ubuntu 8.04 to Ubuntu 10.04, even though this is technically possible. In the future you will be able to switch from Debian 6 to Debian 7, provided that no Parallels Plesk Panel is installed on it.