How can I updated my iPad to the latest update iOS 14.8.

If you attempted to update your iPad and it only updated to iOS 12.5.5, then it is not compatible with the newer iOS. iOS 12.5.5 is the latest it will run. The hardware will not support the newer iOS. If you need the newer iOS for certain apps, you will need to purchase a newer iPad that will support iOS 15.x and later.

Hello,

To update your iPad first of all you need to make sure that you are connect to wifi, make sure that you have VPNs turned off. Go to Settings > General > And then tap Software Update. At this point you may see two different choices. Choose the one that you would prefer to install. Tap Install Now, you may see Download and Install. You will be prompted to enter your password, after entering your device's password you can tap Install now.

Hope this helps!

Brad

Your device - the original iPad Air - is not compatible with iOS 14.8, I believe.

You cannot. As I said the iPad will not support the latest iOS.