When your 3DS or 2DS is able to connect to the internet via a wireless connection (such as your wireless router), you can use the “Update Data” function from the Save menu (when you speak to the Adventurer or from the world map). By updating data, you will receive:
Updated profiles for any friends you’ve already registered, if they’ve recently re-uploaded their profile. This is handy if you summoned one of your friends’ characters and need a new one from them or if they’ve learned new abilities for Abilink.
Up to five random guest profiles from across the globe. These function the same as guests from StreetPass, so you can use their Friend Summon and you will gain an extra resident for Norende for each guest, plus any Nemeses they may have sent. Essential if you rarely get StreetPass tags.
A new Nemesis from Square Enix if they have recently released one and you haven’t already gotten the same Nemesis from them. The benefit of facing Nemeses from Square Enix is that (as far as we can see) you’re guaranteed to receive an item drop after defeating them.
You will also upload your profile, so any of your friends who update data will receive your new profile (and Friend Summon) and other players will too if they’re lucky enough.