i am trying to update my iphone 4 to ios 7 but i can not see general then software update

Update it as described in this article; devices running an iOS version prior to 5.0 can't be updated straight from the device and must be updated from iTunes on a computer. It will be updated to the newest iOS release supported by the device’s hardware, which is iOS 7.0.4 for an iPhone 4.

You would need to be on IOS 5.0 in order to update over the air.

Otherwise plug your phone to your PC and open itunes and update your IOS.