1st Method ( Internet Required ) via Update manager > Start the Update Manager (System > Administration > Update Manager): > The Update Manager should show that a new distribution release (10.04 LTS) is available. Click the Upgrade button to start the distribution upgrade 
2nd Method . Offline Upgrade ( Internet not required)
This method is much faster since it uses offline ISO image to upgrade from HERE.
> Let’s go ahead and Mount the image
sudo mount -o loop /path-to-iso/ubuntu-10.04-alternate-i386.iso /media/cdrom0
> When success, a pop up should appear offering you the option to upgrade using that CD / ISO image.
If for some reason the upgrade dialog doesn’t pop-up, press ALT + F2 and type:
Ubuntu:
gksu "sh /cdrom/cdromupgrade"
Kubuntu:
kdesudo "sh /cdrom/cdromupgrade"
[iso credits: ParaIso]
Via : www.taranfx.com
