how do I install my update to my iPad from itunes

You need a PC with iTunes for Windows installed on it, or a MAC using iTunes or Finder depending on the version of MacOS that is installed. Once you have iTunes installed or if you are using a MAC you plug the iPad into the computer using the cable that came with it to charge it. If you don’t have the port needed that is on the end of the cable then you can get a cable that will attach to the computer and your iPad (like a USB to Lightning or USB to USB-C or whatever is needed to fit both devices). Once you get it connected it should come up in iTunes where you can then see the iPad and select to update it through there.

You can see more information on how to do this here Update your iPhone, iPad, or iPod touch with iTunes - Apple Support

If your iPad is capable of update 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

Be aware that while an iPad may be capable of update, in some circumstances you may need to use a computer to perform the update. To do so, you will need access to either a Window PC (with iTunes for Windows installed) or a Mac (with iTunes or Finder - as appropriate for the installed version of MacOS). Ensure that your installed version of iTunes has been updated to the most recent version; the essential device drivers are included.

Download and use iTunes for Windows – Apple Support

Update to the latest version of iTunes – Apple Support

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

Update your iPhone, iPad, or iPod touch with iTunes - Apple Support

Update your iPhone, iPad, or iPod touch with the Finder - Apple Support

If you have a beta profile installed, ensure this has been removed from your iPad - as, otherwise, installation of production software updates may be inhibited. This support page provides the necessary information to remove the beta from your iPad:

How to uninstall iOS beta software - Apple Support

You should note that for your iPad to install an available update, its battery must be charged to at least 50% capacity - and/or be connected to its Power Adapter. Similarly, the iPad can only be updated over a standard WiFi connection - or be updated by a PC or Mac using iTunes or Finder - over a USB connection.