The first thing you need to do is post in the forum most likely to be able to answer your question. This is the iWork for iOS forums. I have asked that it get moved to the desktop forums.
I beleive you have to completely uninstall the iwork trial, then install the full version. but someone on the desktop iWork forum would be able to confirm this for me.
You need to delete the trial & then reinstall from the boxed DVD or the Mac App Store. The files to delete are the iWork ’09 folder from the main HD > Applications; the iWork ’09 folder in HD > Library > Application Support & the individual iWork application plist files found in HD > Users > (your account) > Library > Preferences for each user.
Yvan Koenig has written an AppleScript that removes the files. You can find it on his box.com account in for_iWork'09 > other_iWork'09 items > uninstall iWork '09.zip.