i want to upgrade ios 10 my iphone4

You can't, sorry.

Latest supported iOS version on iPhone 4 is 7.1.2

Latest supported iOS version on iPhone 4s is 9.3.5

Regards

Giulio

You cannot.

Update the iOS software on your iPhone, iPad, or iPod touch - When you update you will only be given one update selection which will be the highest available iOS version supported by your device. If it says no update is available and you need a higher version you will have to buy newer equipment.https://support.apple.com/HT204204