Good morning, I am trying to update through the terminal but it reads

W: Duplicate sources.list entry http://archive.canonical.com/ubuntu/ precise/partner i386 Packages (/var/lib/apt/lists/archive.canonical.com_ubuntu_dists_precise_partner _binary-i386_Packages)
W: You may want to run apt-get update to correct these problems

...I am running the command asked for...what to do?
I am using Ubuntu 12.04