How to uninstall Windows from a Dual Boot system? [duplicate]

Since your question is really several questions, I'll divide my answer into parts. Unfortunately I'm sitting on my windows laptop now, so I can't generate any screenshots or even test the programs and see where all the options are - if there's something you can't find, don't hesitate to ask.

1. How do you remove Windows from a dual-boot configuration without having to go through another Ubuntu installation?

When you installed Ubuntu alongside Windows, the installer created (at least) one new partition on your hard drive, on which Ubuntu was installed. Windows usually occupies two partitions (one for the boot loader and one for C:\), so that would mean you now have three.

If you, when you start Windows, have any files you want to save on C:\, you need to back them up before you continue. One way to do that would be to simply copy them to the Ubuntu partition, which can be done by following these steps:

1. Boot your computer into Ubuntu
2. Open Nautilus (the file browser, equivalent of Explorer in WinXP) and find your Windows partition in the device list on the left. Click the device.
3. Find your files on that partition, and copy them to somewhere you can find them. If you put them in ~username/backup they won't be in anyones way.

Next, you want to remove the Windows partition entirely, in order to free the space so Ubuntu can use it. This most easily done with GParted.

1. If you don't have GParted installed, install it by opening a terminal and entering
   sudo apt-get install gparted
2. Open GParted by typing gksu gparted &
3. In GParted, locate the Windows partition, select it, delete it and click Apply. Warning! After you do this, the data on your Windows partition is lost forever!
4. Mark the empty space, find "Create new partition" somewhere and choose an appropriate name ("Data", for example). If you intend to only use Ubuntu in the future, you can format the drive as ext4 - but if you may want to move back to Windows you should probably choose NTFS so Windows can use that partition. NTFS works almost as well as ext4 under Ubuntu, but there are a few quirks - for example, Google Chrome (and Chromium) cannot download files to an NTFS drive.
5. Open "Storage Disk Manager" (for example by searching for it in the Unity search box). Click the partition you just created (you might have to look around for a while and click several of the /dev/sdaX options...) and configure it to mount on startup. Note the mount point that is shown - this is where on the Ubuntu file system you will access the files on the partition from now on.

Instead of creating a new partition and mounting it, you could also start from a Live CD/USB and expand the Ubuntu partition. However, I would strongly recommend having a separate partition for stuff you want to keep regardless of OS version. My reasons for this will become apparent in the next part of this answer...

2. Are the Ubuntu updates safe to take?

If, by "Ubuntu updates", you mean the updates provided by the package management system every now and then, then yes, they are safe and stable. However, the upgrade process between Ubuntu versions (for example from Ubuntu 11.04 to 11.10) is not always as stable, and it is usually recommended to install the new version from scratch instead of upgrading. (A fresh install is also usually a lot faster...)

Because this is so, it is often useful to have separate disk partitions for stuff you want to keep between upgrades. On my Ubuntu machine I have separate partitions for /home, /boot, and /data - and that has saved me many times when I screwed up some weird configuration file and had to reinstall Ubuntu to fix it.

3. Is there any such thing as a restore points in Ubuntu?

No, there is not. Therefore, it is extremely important that you take care and backup any sensitive data that you do not want to lose before you alter your system.

1. Uninstalling an OS usually means deleting the entire partition. Use the Ubuntu live CD/USB to expand the Ubuntu partition afterward.

2. All offered updates are tested and should be quite safe to install.

3. No restore points.