|"Can I use my tower dvd deck to upgrade W7 in my netbook ?"|
No. There is no way to connect it to the netbook in a way that the netbook will detect it, plus a standalone tower dvd player cannot read Windows data discs.
You will have to buy an external dvd-drive that plugs into a usb port and hope that your netbook can boot from it (with the Win7 DVD in the drive).
Another consideration is the netbooks's CPU or processor. Most netbook's are fitted with an "Atom" cpu which is barely powerful enough to run Windows 7. That's why the factory usually installs Windows XP on them.
And last but not least, you will have to check your netbook manufacturer's website to make sure they have Windows 7 drivers for your model. If they don't, there is no point installing Windows 7 because some of the hardware won't work (eg, sound, graphics, wireless adapter etc.)