how can i update my keynote 8.1

You can only update to the current version of Keynote, not an earlier version

To install the latest version of Keynote you require the following:

1 - a compatible Mac computer from this list:

• MacBook (Late 2009 or newer)
• MacBook Pro (Mid 2010 or newer)
• MacBook Air (Late 2010 or newer)
• Mac mini (Mid 2010 or newer)
• iMac (Late 2009 or newer)
• Mac Pro (Mid 2010 or newer)

2 - Mac OS 10.13 or later installed

To install Keynote, open the Mac App Store from the Applications folder sign in with your Apple ID then in the search box enter "Keynote"

I cannot get Keynote to upgrade. The asterisk just spins. I've updated to High Sierra but when I go to the app store and click to update Keynote the asterisk just spins and spins. (I only have 8. on my home computer but I have 9.2 on my work computer and I want to get them aligned). What am I doing wrong?

Easiest thing to do would be to copy keynote from your work computer on to your home computer