The screenshots are taken with iOS 7, however these instructions are the same for other versions of Safari on iOS.
Tap the "Settings" icon on the home screen
Return to the Home Screen by pressing the round button underneath the screen. You will see the grid of icons. Then, find the "Settings" icon and tap on it.
Scroll the Settings sidebar until you can see the Safari icon
The Settings app doesn't show the Safari icon on the side bar by default, so it's necessary to slide it a bit until you can see it.
Tap the "Safari" menu option
The right side of the screen will change to show you the various settings options available for Safari.
Scroll the "Safari" settings section down to the "Advanced" option.
Once again, the section you need to go to is further down the screen; drag the screen up with your finger until you see the "Advanced" option.