http://ubuntuforums.org/showthread.php?t=435851 ,go to this link it will show
you how to renew and release

A wired connection will just work in Ubuntu, unless you have been using static
ip addresses and it sounds as if you are not. A wireless connection may take
some tweaking because the settings were saved. Delete any old connections and
set up your wireless network once again. I have replaced my router numerous
times and have gone from cable modem to DSL and there aren't any differences
between Windows and Linux, except when it comes to the way it handles wireless.

Go to System>Administration>Network click on the
Unlock button and enter your admin password. On the Connections tab,
double click on your Wireless connection. If roaming mode is enabled,
disable it. Check your other settings and click OK. When you close
your Network Settings window, it should find your router.

If thats a new device (a recent device) that Ubuntu 8.10 doesn't recognize, you
still have the possibility to update your distro (Better than update the kernel
only).