How to turn on/off my 4g on iPhone4s?

I have the iPhone 4S and have the 4G and I use AT&T so if I'm not connected to Wi-Fi how can I make sure my phone isn't using 4g? Besides airplane mode cause that just turns off everything including texts and calling. So how do I turn on/off 4g?

OK, let's start off at the beginning…
The iPhone 4S does not have 4G capabilities in it. It doesn't have the right chip for 4G connections, so it's not going to be able to use a 4G signal.

Next thing is what is 4G - it is a type of cell signal - nothing to do with Wi-Fi.
Your iPhone 4S will work on 3G and EDGE signals.
3G will allow for faster data downloads, but it will use more battery power, so the battery won't last as long.
If you want to switch off 3G, go to Settings > General > Mobile Data. The second option is "Enable 3G". You can switch 3G off there.

You are not charged extra for using 3G instead of EDGE, so unless you want to save the battery, don't bother switching 3G off.