Trying to do a software update on my ipad and I cannot install the update. I never had this problem before.

If your iPad is capable of being updated to a more recent version of iOS/iPadOS than is currently installed, these support pages outline both the available methods by which the update can be performed - and troubleshooting should you experience difficulties:

Update your iPhone, iPad or iPod touch – Apple Support

If you can't update or restore your iPhone, iPad or iPod touch – Apple Support

If your iPhone, iPad or iPod touch won’t update - Apple Support

iOS update and restore errors – Apple Support

Your iPad Air2, with iOS 12.4 installed, is too far behind to be able to update from iPad settings. You must instead connect your iPad to a PC (with iTunes installed) or a Mac (with iTunes or Finder - as appropriate for the installed version of MacOS). Once connected, you’ll be able to use the computer to update iOS to the most recent version of iOS supported by your iPad.

Update your iPhone, iPad or iPod touch – Apple Support

Update software on iPhone, iPad or iPod touch in iTunes on PC - Apple Support

Kiawife1 wrote:

I have the iPad Air 2 and using the 12.4 version

That's a very old iOS version, and you might have many difficulties to update your iPad Air 2 wirelessly (via Wifi).

To update it to the latest iPadOS version (now 14.4.1) I suggest that you update it using a computer running iTunes (PC) or iTunes/Finder (Mac).

Regards

Giulio

On what iPad model? What iOS version is currently running on it?

What happens when you try to update your device?