how to change from unity DE to LXDE in Ubuntu 13.04

[hotwaxdripping]

I did a wubi.exe install of Ubuntu 13.04 on a windows xp computer and I really like Linux over windows. But I'm trying to squeeze a little faster performance out of my computer (Dell Optiplex 745 with Core 2 duo 2.13ghz cpu and 8Gb of DDR2.) by switching to LXDE. I tried

sudo apt-get install lubuntu-desktop

I asked me for the CD I used, but I used and extracted winrar file. the exact response I get in terminal is

Media change: please insert the disc labeled
 'Ubuntu 13.04 _Raring Ringtail_ - Release amd64 (20130424)'
in the drive '/media/cdrom/' and press enter

am I having problems because I did a wubi.exe install? How do I switch to the lighter weight LXDE desktop? Thanks for your support (the Linuc community is great!)

[snowpine]

You should uncheck the box for the CD-ROM in your Software Sources so that your Software Center can download the packages from the internet.

https://help.ubuntu.com/community/Repositories/Ubuntu

[mysteriousdarren]

I'd do a clean install of Lubuntu and go from there. Wubi can run into problems and has not worked for me very many times.