Q: How do I transfer my contacts from old iPhone to new iPhone

I'm upgrading & trading in iPhone (5 for a 6+)

I've been told to delete all my info on the old phone - this is ok I can back up the apps - but how do I transfer my contacts?

I won't have both phones enabled at the same time as the old one will be'empty' of all info when I hand it in

Any help would be appreciated,

Andy