removing XP and reinstalling a full version of Ubuntu

Please back up ALL your important data under windows then follow steps outlined here: https://help.ubuntu.com/8.04/switching/installing.html

This will also help: http://www.psychocats.net/ubuntu/installing

Please download the iso image please read my install note below, then

1) boot your pc entirely from the Ubuntu live install cd (you must not see start Windows) select try Ubuntu
2) Open the menu System→Administration→Partition Editor gparted
3) select the Linux partitions, right click on it, and delete them (to apply changes press on the green "V" top button)
4) close gparted

5) click on install Ubuntu icon on desktop and when requested please select install Ubuntu on the unallocated space.

Hope this helps

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Here some general note on install Ubuntu and howto to get a good ubuntu iso cd image (.iso) to burn on a cd:

- Here the steps to install Ubuntu 10.04.1 https://help.ubuntu.com/community/GraphicalInstall

- Here install Ubuntu video http://www.youtube.com/watch?v=XaqaDZZ_P0g&feature=fvw

Below there are some intructions to:
1) Ubuntu prerequisites...
2) download the iso...
3) check the md5sum of the iso image, please don't forget to check...
4) burn the iso image to a cd ...
5) install Ubuntu using the self made cd ...
6) trouble with installation ...
7) Get a good Ubuntu manual ...

The main ubuntu site is this: www.ubuntu.com and the download location is this
http://www.ubuntu.com/desktop/get-ubuntu/download

1) Ubuntu prerequisites: https://help.ubuntu.com/community/Installation/SystemRequirements

Ubuntu 10.04.1 release notes: https://wiki.ubuntu.com/LucidLynx/ReleaseNotes

https://wiki.ubuntu.com/LucidLynx/ReleaseNotes/ChangeSummary/10.04.1

If your ram is less than the recommended amount, you won't be able to install with the graphical installer,
but you might be able to use the Alternative cd, where you can use a text based installer - that uses less memory.
If your machine does have plenty of ram, you might want to try running Memcheck (which is also an option from the live cd, see below)
to just make sure your ram isn't failing.

2) please download the 700 mb file http://www.ubuntu.com/desktop/get-ubuntu/download simply press on download button
To avoid download errors download the desired ubuntu iso install cd image using the torrent protocol.

- if you are using Windows please install a torrent client i suggest you http://deluge-torrent.org/
and download the iso using a .torrent link from here:
http://releases.ubuntu.com/10.04.1/ubuntu-10.04.1-desktop-i386.iso.torrent

3) PLEASE BE SURE TO CHECK the md5sum of downloaded file to be sure it have no error https://help.ubuntu.com/community/HowToMD5SUM
Only if the md5sum number match with this: http://releases.ubuntu.com/10.04.1/MD5SUMS go to the next steps.

4) burn the iso image onto a cd, to do it install and use http://infrarecorder.org/?page_id=5 burn the cd at lower speed you can do and activate the data verify

5) insert the self made install cd into your pc cdrom drive and reboot your pc. YOU MUST NOT SEE Windows starting and you can try Ubuntu from cdrom and then install it

6) If you have trouble with installation (the system freeze or you can't complete it) be sure to read the above suggestions, then:

Please boot entirely (you must not see windows starting) from Ubuntu live install cd and when the system start to boot from cd you will see two bottom screen icons (keyboard and man inside circle ) please press space (choose your desired language) then a screen textual center menu will appear to you with this items in it:

Try Ubuntu without installing
Install Ubuntu
Check disc for defects
Test memory
Boot from first hard disk

Please select "Check disc for defects" and press enter to test if your cd-driver can read in a good way the live install cd... or if the install cd have some defective file in it.
Then please also perform a Test memory to be sure your pc RAM memory have not any issue

If you get a blank screen at boot after install or booting from the Ubuntu install cd please read:

http://www.ubuntugeek.com/how-to-fix-ubuntu-10-04-lts-lucid-blank-screen-at-startup.html

If you have trouble with intel8xxx graphic cards:

please try this: https://wiki.ubuntu.com/X/Bugs/Lucidi8xxFreezes

7) Ubuntu Manual, it's very informative: http://ubuntu-manual.org/
Click on the "download Button" to download the latest PDF version.

Reading your question better Ubuntu was installed using Windows (Wubi installation)
So before to do what i answer you above previous post please remove the Wubi installed Ubuntu

If you have installed Ubuntu via Wubi please uninstall it read
http://wubi-installer.org/faq.php and https://wiki.ubuntu.com/WubiGuide

Before uninstalling wubi - make sure you back up your root.disk - this contains all your Ubuntu data and settings since starting to use Ubuntu. It's also possible to migrate a wubi install to a direct partition install as well, without losing data or customization (http://ubuntuforums.org/showthread.php?t=1519354)

If you don't need to keep current setttings and don't want to keep XP, it's easier just to reinstall over the entire drive (with your data backed up on an external USB drive)