This source is from Usa offical psp web site
Update using a UMD*
Use the update data included on a UMD* to perform the update. Click the link above for update instructions.
*As of July 27, 2006, this method is only available for updates up to version 2.60.
Does this mean it only goes up to 2.60 on a UMD so 2.6 is the limit. Or you need to update using the GAME>UPDATE to play the game if the UMD was 2.8.