Ok bro.So here what i would suggest.
But after that you won't have windows any longer and only Ubuntu as your only OS.And the process can't be reversed(Please note that).
First of all if Windows is working properly and you want to only keep Ubuntu as your OS then you have to clear your whole hard drive.
That means delete all the partitions i.e the local drives(E:/, F:/) and others by refering to this site(don't delete the C drive now it's not necessary).
http://www.disk-partition.com/help/clear-disk.html.
Also there are other websites on google which you can refer to delete all the partitions completely.
Now in case when you don't have any drives except the C drive and you see that it's not taking the whole capacity of your hard drive then just make sure that all the space is unallocated which will be after you delete the partitions.
(It will be better if you install Ubuntu 14.04 because right now it's the long term support release).
After that when you are installing Ubuntu from your flash drive or cd, you will probably see 5 options.
Now as said previously you won't have your windows partition after this step.The only OS will be Ubuntu.So select the option which says install Ubuntu and erase the disk completely.
It will erase everything and after that the steps are easy you will be able to understand them.
So I guess it will clear your doubts.
Don't be nervous.Install Ubuntu for now.After doing the whole process of installing OS once you will be able to understand it and it will be no problem when you do it again.
So try it.