There are 2 ways in uninstalling softwares.

1. Open Control Panel
Start - Control Panel (XP)

2. Add/Remove Programs

3. Find the software installed. and click 'Remove' or Uninstall

Another way is using the uninstall program package on the software itself.

1. Start - Programs - Find the name of the software.

Point your mouse and see if there is 'Uninstall' ..click this menu.

It is not safe to delete the 'Entire folder' of the software. So it is recommended to use the two steps.

Edit:
If you are referring to a Microsoft Windows OS installed in your PC. Installing this will make your computer disabled (unless you are about to install new OS).