[xubuntu] Please help-installed ubuntu yesterday,want to change to xubuntu

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http://ubuntuforums.org – Hi I installed ubuntu yesterday on my old lappy with a bootable USB. I have tried Unity 2d and still it isnt coping well with it, so I have decided to try xubuntu instead. Have downloaded xubuntu image and used the pendrive linux thing to create the bootable usb(i formated it too) When I boot the USB, xubuntu comes up on the screen but will not either boot or install. Shall I retry and do the usb again? Will I be able to erase ubuntu like I did with win xp(OS pre ubuntu)? Thanks in advance (Hardware)