my son is still using iphone4 with iOS4. Any method to upgrade it to iOS6 or 7

The iPhone 4 can upgrade to iOS 7.1.2

If I remember correctly you won't be able to do it using the wireless method (could be wrong about that) but the iTunes method in the following link will do it: Update the iOS software on your iPhone, iPad, and iPod touch - Apple Support

I don't know what iOS 4's interface looks like. Is there a Settings > General > Software Update option or something like it? If so just select it and it should present you with Download and Install. The highest version of iOS compatible with your phone will download.

capricorn2yk4 wrote:

how to upgrade iOS4 to iOS6 on my iphone4.

connect phone to computer

launch iTunes

click Update

Easy

As provided, open iTunes, connect iPhone, click update