How do I update my iPad 2 to work 4G

You don't. The Cellular hardware in an iPad 2 cannot be accessed much less replaced.

The bets you can do is get a Mifi device from your carrier, which can connect to 4G/LTE networks and provide a Wifi connection to your iPad from that.

BDAqua wrote:

I was wondering if one of those would work on an iPad, thanks.

The work just fine. In fact, I got a WiFi iPad because I already had a wireless hotspot to use it with. The iPad will also work using the hotspot feature of a smartphone.

If you mean 4G speed, I doubt there's any way, unless the Dock Connector to USB would be able to use some auxiliary Wifi device.

Many wireless carriers sell portable hotspots. Cancel your cellular plan on your iPad and get one of those instead.

I was wondering if one of those would work on an iPad, thanks.

They will work with pretty much any device that connects to WiFi. Note that I'm talking about the stand alone devices, not the ones that plug into a USB port.