No update centre?
sudo apt-get update ; sudo apt-get upgrade
is all you need!
Unless you're a "fly by the seat of your pants" kind of guy in which case
apt-get update ; apt-get upgrade
Does the trick, and handily leaves you in Super User mode for performing tasks that shouldn't be run in super user mode!
[confession]I'm only acting out because I'm jealous[/confession]
[big confession]The server I run at home that has debian on it doesn't have sudo installed, so I use su to enter super user mode, and normally just stay in super user mode till I log off![/big confession]