Can anyone show me the way (step by step comands)?
Probably somebody can - not me though
- until then:
AFAIK this computer comes preinstalled with XANDROS linux - is that true?
If this is so:
check out their website on what they use for software-management (installing updates, installing new software...) how it is operated and what software you can download.
They have some kind of graphical tool for it.
I've read that it is possible to use the software-repositories of other distributions (Ubuntu/Debian) - but this is not trivial.
If you really have XANDROS installed you are a bit limited and tied to them and don't have all the choices a "normal" distribution has to offer.
But there are ways to install a "real" distribution instead - if you desire and are willing to.