Good afternoon charity277,
Welcome to the Apple Support Communities!
I understand you have some photo projects in the Photos application on your Mac that you would like to print again. Having just created a 100-page photo book myself, I understand how much effort goes into this. The software update that is needed is for your Mac. There is no cost to upgrade the operating system on a Mac, but please make sure that you back up your computer using the Time Machine application to an external drive before you do so.
Apple is no longer providing printing services, but there are a number of companies such as Mimeo Photos that have taken over that role. I'll include some resources below to that will explain the changes in more detail so that you can decide if you want to go that route.
Back up your Mac with Time Machine
How to update the software on your Mac
Create and order print products in Photos with Project Extensions
Take care.