Hard resetting an iPhone 4 is very easy and this video will talk you through the process.
All you need to do is to press two buttons at once and hold – the power button up the top and the round home button on the front. The video demonstrates how to do this most effectively and you’ll find that it takes only seconds to reset your phone.
Do note that when you reset your phone you will lose ALL your data. Please make sure you have backed everything up first and that you are happy to lose anything left.