You need to follow the following steps to install windows :
1. Insert the windows DVD in your computer or if you want to boot it from the USB then insert a windows USB.
2. Restart your computer and press F12 or other function keys suggested by your computer to enter the Boot Menu.
3. Once in the Boot menu Select Boot from CD, or Boot from removable devices, if you want to boot from USB.
4. Windows will start booting from DVD or USB as selected by you.
5. Follow the screen instructions.
6. Windows screen will appear select the language and time and input method and press next.
7. A new install window appear, press install now.
8. A new window asking the accept license term will appear select accept and press next.
9. A new window will appear, with two option first one is upgrade, and other one is custom, select custom.
10. A new window will appear, asking you where you want to install the windows.
11. You will see all your hard disk partitions. You need to delete all these partitions. Deletion will delete all your system data. Select drive options. Here you will see many options. select the drive you want to delete and press delete.
That partition of hard drive will be deleted. Repeat this step till only one drive remains showing all the hard disk space.
12. Now select New option and enter the disk space size you want to create. Create 2 or three disk partitions. A 100 GB partition may be a size of 100000 MB.
14. Now you will see all the partitions you created.
15. Select the partition in which you want to install windows and format it.
16. Press next and windows will start installing windows.
This process can be used to install any new windows.