Older mac can't upgrade/buy newest version pages

Question

late 2009 iMac running yosemite 10.10 gets this error message when attempting to upgrade Pages to the latest version thru the Mac App Store.
"Can't upgrade as this app was purchased by a different user, or was cancelled previously.  "
This is a new userid on a machine that had been used by someone else previously who is long gone and left no userid and password information.
Only Pages copy on the machine is Pages '09 Version 4.3 Build 1048.
Any advice on how to get the system to allow them to buy the newest Pages version?

Answer 1

You will need to back up that Pages ’09 version for safe keeping as it has 110 more features/functionality than any version of Pages v5. The latter was a brand new application in Oct. 2013, and Apple barely added any functionality from the Pages ’09 application. Pages v5 has had numeric updates with almost nothing to show for improvements.
Someone previously acquired OS X for this machine, and registered the installation to their Apple ID as administrator. Gone or not, only they can acquire application updates from the OS X App Store using that previously associated Apple ID. Only the administrative account on the Mac can install system and application software.
To free this machine from this prior Apple ID lock, you will need to reinstall OS X Yosemite, and associate this Mac's administrator account Apple ID with the new installation (on a fresh boot after install). Any OS X App Store applications previously acquired via another Apple ID are not available to you. Once the reinstallation is complete, then signing into the OS X App Store with the administrator's Apple ID will permit application purchases, downloads, and software updates by that administrator.