I have installed Ubuntu 12.04 , but now I am not satisfied as it has taken more space 100 GB. Since I have to use Windows more often, I found that I am unable to see the files of Ubuntu when I open the Window. Therefore I want to give smaller file system (repartition). Please guide me so that I can reduce the volume of my Ubuntu file system.
Use a Live CD or a Live USB to run an app called GParted. A Live CD (or USB) is an installation CD (or USB), but when the option pops up, select "Try Ubuntu without installing".
Then, when the boot process is complete, run the GParted app from the Dash Menu. It will permit you to change the size of your disks.
When you installed 12.04, did you choose the partition size, or did you leave it to the installer?? Anyway, if you run the partition tool called Gparted you will be able to see how your hard disc is split up, and also to resize the Ubuntu partition to suit your needs. You may need to install Gparted from the Ubuntu Software Centre if it is not already in place.