Can anyone help me to find the way to use a CD writer as a DVD Writer.

You can't. They are physically different pieces of hardware.

1. Buy an inexpensive DVD-Writer:
   HP dvd1035i DVD Writer (Retail) - 48x CD-R, 32x CD-RW, 20x DVD±R, 8x DVD±R DL, 8x DVD=RW, 6x DVD-RW HPDVD1035I at TigerDirect.com
2. Open computer (2-3 screws on back/side)
3. Unplug data cable and power cord from back of CD drive
4. Remove the 2-4 screws holding CD drive in place and discard
5. Insert DVD writer, reapply screws, data cable and power cord
6. Close the computer
7. Reboot, inserting the DVD-writer's install CD after system detects the new drive
8. Install the new drivers
9. Reboot again
10. Install additional software/utilities that came with new unit (off the CD) if desired
11. Enjoy new DVD writer