I installed Ubuntu 14.04 from a CD-ROM. I selected the option to install Ubuntu along side Windows. I did not understand the slider for the partition for the install, so I just took the default. I discovered that half the of the available disk space was reserved for a Windows partition, and the remaining partition for Ubuntu. How do I extend/re-install Ubuntu to make use of that partition is reserved for Windows?
OK, you are basically asking two questions and I will provide answer for both. Your problem is that apparently you accepted the default Ubuntu installation partition recommendation and now you want to give Ubuntu more space on your hard drive, correct? Answers:
Without having to re-install Ubuntu, you can resize both partitions by booting into a Live CD (like the one you used to install Ubuntu), just make sure to select "Try Ubuntu" instead of "Install" when the choice appears. Then, go to the top left corner and hit the Ubuntu logo button, then type GParted. When GParted opens up, you can re-size the Windows installation to make it smaller. After this, make the Ubuntu installation bigger by filling in the empty space that the Windows installation left and wait for the process to end. Exit the Live session and your partitions should be the size you want them. However, since Ubuntu has already been installed, this may (most likely) take longer than doing a fresh install which ultimately is what I recommend.
If you just barely installed Ubuntu and you don't have any work already saved in your installation, just go ahead and re-install. It's the easiest and quickest way. If you've already been working on Ubuntu for a while, try to save all that you can to an external hard drive or to a cloud service like Dropbox before doing the fresh install. Just make sure that when you re-install you first delete the Ubuntu partition with GParted, then you make the Windows installation the size you want it to be and leave the empty space for the Ubuntu installation. The installer should automatically choose the empty space to install Ubuntu.