My ipad is old update is 12.5.7 how can i uprgate my ipad to ios 16 my ipad is ipad 3 air

Only the iPad Air 3, 4 and 5 are capable of updating to iOS 16. The hardware in the older models are not capable of updating to 16. If you select Software > General > About, you will see which model you have.

iPad models compatible with iPadOS 16 - Apple Support

I need emails on my iPad and I have to have ios16

How do I updat my iPad iOS

Select Settings > General > Software Update. If your iPad is eligible for an update, you will be prompted to do so.