The situation is you installed Ubuntu along with Window, and later remove Ubuntu and install Xbuntu, however, ubuntu can still be found in boot menu of window, how can I remove it?
1. Go to official site and download the newest copy: http://www.ubuntu.com/download
2. Create a bootable USB for installer: http://www.ubuntu.com/download/desktop/create-a-usb-stick-on-windows
3. Turn off your computer and turn it on again, make sure that your laptop is boot from usb. (If not, then you can reboot your laptop and press F-12 or F-8 or something like that, depending on your laptop, and set up the laptop to boot from usb)
4. As your laptop is booted from usb, you can choose something like “try ubuntu” and go into the ubuntu system. from the desktop, you can find something like “install ubuntu” and you can start installing ubuntu.
5. Follow the instructions and finish the installation. Note: You will choose partition for your ubuntu, choose whatever you have in hard disk 😛 your preference.
0. A good guide to show you installing ubuntu14.04 on a window 8.1 machine (also take care the boot issue later after installation)
1. If you have one disk and want to do partition:
2. If you have two hard disks: