Hi! I'm new to UBUNTU!

[Maurice McCarthy]

Jorge

Perhaps I'm teaching granny to suck eggs but what is in your file
/etc/apt/sources.list ?  I have

= = =
deb http://gb.archive.ubuntu.com/ubuntu/ lucid main restricted
deb-src http://gb.archive.ubuntu.com/ubuntu/ lucid main restricted

deb http://gb.archive.ubuntu.com/ubuntu/ lucid-updates main restricted
deb-src http://gb.archive.ubuntu.com/ubuntu/ lucid-updates main restricted

deb http://gb.archive.ubuntu.com/ubuntu/ lucid universe
deb-src http://gb.archive.ubuntu.com/ubuntu/ lucid universe
deb http://gb.archive.ubuntu.com/ubuntu/ lucid-updates universe
deb-src http://gb.archive.ubuntu.com/ubuntu/ lucid-updates universe

deb http://security.ubuntu.com/ubuntu lucid-security main restricted
deb-src http://security.ubuntu.com/ubuntu lucid-security main restricted
deb http://security.ubuntu.com/ubuntu lucid-security universe
deb-src http://security.ubuntu.com/ubuntu lucid-security universe
deb http://security.ubuntu.com/ubuntu lucid-security multiverse
deb-src http://security.ubuntu.com/ubuntu lucid-security multiverse

# deb http://download.virtualbox.org/virtualbox/debian lucid non-free
# disabled on upgrade to lucid
# deb http://deb.opera.com/opera/ sid non-free # disabled on upgrade to lucid
= = =

If you add or remove a deb source then you can run

sudo aptitude update && sudo aptitude safe-upgrade

just as you would in Debian and everything should work out fine.
(According to Joey Hess you should always use aptitude in preference
to apt-get. See
http://linux.derkeiler.com/Mailing-Lists/Debian/2004-04/3181.html and
so far as I know that advice remains good.)

In Ubuntu the Update Manager normally does all this for you.

Regards
Maurice