Unable to Update Ubuntu 9.10

I am using an HP system with pre installed windows vista. Recently I installed ubuntu in to my system, but found that I was not able to update it, as each time when i try to update, the message comes, "Please insert the disk labeled; Ubuntu 9.10_Karmic Koala_-Release i386(20091028.2)in drive/cdrom/"; and once I put the CD, its not moving further, and getting struck or showing unable to mount the CD. Please help me with this and advise me with methods to solve this issues.