I'm not sure, Malcolmjean. I'll defer to Apple's recommendations on that one. Check out this link:
http://support.apple.com/kb/HT4623?view ... cale=en_USIf you're running pre-iOS 5, scroll down and expand their instructions for "Update your device using iTunes".
Also check out their link in "Additional Information" which says "Ensure that your device is backed up to iCloud or back up with iTunes before updating. Find more information about backing up your iPhone, iPad, or iPod touch."
In any case there should be some decent info on that page.
Good luck!
Eddy