I downloaded the xcode from web and installed after that i cant find any update regarding xcode on App Store. How to make the app store show updates about the xcode in app store.
If you manually downloaded Xcode from https://developer.apple.com/downloads/, then the App Store app isn't aware that there's an Xcode that needs to be automatically updated. The App Store app only keeps track of store apps it downloaded and installed itself.
You need to either download Xcode from the Mac App Store directly or you need to keep watching the http://developer.apple.com/xcode page to get informed of updates.