Basically, this means that in your /etc/apt/sources.list, you have the same repository listed twice.
This isn't exactly an error, it's a warning, and it is pretty harmless one too.
However, if you wish to stop these warnings appearing, read below, understand, then decide what you feel is best. If you don't feel comfortable with either, then don't do this. The messages you get are a warning, and isn't even remotely harmful to your OS.
First things first: Back up your /etc/apt/sources.list file in case you make a mistake. Open up a terminal, and run:
sudo cp /etc/apt/sources.list /etc/apt/sources.list.backup_warning
(I tend to add descriptive titles to my backups instead of numbering them in case I need to go back to them later)
Now you have two ways to fix this
The simple way: Open up the Ubuntu Software Centre. On the Menu bar, click on Edit and go all the way down to Software Sources.
Click on the Other Sources tab and maximise the window to prevent removing the wrong repository. Go through the list until you find the repositories listed above and then untick. Then press close and allow the Ubuntu Software Centre to refresh packages.
If you have done this right, you should have no more warnings.
The mildly complicated way: Open up the terminal. Type
sudo gedit /etc/apt/sources.list
and then find those URLS listed above and place a hash ('#') symbol before the lines. Again, if you have done this right, you should have no more warnings.
Personally, I'd recommend you go down the simple way, as there is less chance of shooting yourself in the foot and damaging your repository updating mechanism. Or failing that, don't make a single change. Your system is absolutely fine the way it is.