Guys, I need some help,
What do I have to do to upgrade my rank?
Do I need to scan QR codes in order to have bases in my game and capture their flags?
Yep. You require to wait until the next day via QR codes, though. Changing your 3DS time will only make you wait for another 24 hours.
Another method is by passing by others, just leave your PSS connected to the Internet and wait for your BuzzNav to give you new notifications, then open it and tap on the mailbox. You'll get secret bases and from there you can visit them and immediately snag their flags.
Sometimes when you recruit people that already have a good amount of flags, they'll give you some. One of mine gave me 9 flags earlier.