There are two ways of resetting your phone, hard and soft. Hard reset is done by using the hardware keys like power key and volume key and Soft reset is done by using the software. If you are able to go to Settings -> General -> Backup and reset then you could do a soft reset. There are scenarios where your phone gets hanged and not in a position to start the phone you may need to go for hard reset.
Let’s see how to do this,
To do a soft reset, go to Settings -> General -> Backup and reset and from the Backup and reset screen tap Factory data reset before that tap on Back up my data option to take a backup before you do the reset.
When you tap the Factory data reset it will take you to the Factory data reset screen where there is button Reset device. This will erase all your data and restart your phone.
To do a hard reset, remove your battery and place it back. Then Turn on the phone by pressing Volume Up + Home + Power buttons at the same time. It will show a list of option, from the list select reset and confirm. You could use the up and down volume buttons to move around the list. This will format your device completely.