go to settings, apps, last tab and remove data of update app. It will remove knowledge of choice never remind again.
if that doesnt help or instead hookup to kies and let kies update it.
if he changed rom in past or csc or otherstuff then you need pc odin way. Dr ketans stickied thread in original develment section. Before root and backup efs if thats the case. While you at it flash save custom kernel and in recovery wipe cache, factory reset, in advanced Dalvik, then in mounts format all (be sure all you want to keep (pictures, contacts and take out sd card). Then flash away
all at own risk.
you will find the how to do that across this forum the moon, Uranus, Jupiter and back, search, read first posts an thread of threads and you will succeed.