I've gotten in touch with Apple Support. This is what they suggested which worked for me.
My programs were bought long ago in 2009 on CDs and I live in Germany, so my computer is set up with German as the main language. So if anyone has a similar situation it might work.
Go to System settings > Languages & Region. Change the primary language to English. Close System Settings. You will get a prompt to restart the computer. Do so. Once your computer is up and running again, go to the App Store and you should see all the iWork and iLife products as free updates.
After the update is completed (it took a very long time), you can return to System Settings and change the primary language back to where you had it and restart the computer again.
The apps do not overwrite iWork 09. There is a separate folder with all those original programs. I don't intend to delete them and will probably continue working with them as long as I can. I've opened up a layout document that I'd made in the new pages and it wasn't interpreted correctly.
I hope this solution helps.