Wheezyを最新状態に更新
$ sudo apt-get update
$ sudo apt-get upgrade
$ sudo apt-get dist-upgrade
aptのリスト情報をJessie用に修正
$ sudo vi /etc/apt/sources.list
deb http://mirrordirector.raspbian.org/raspbian/ jessie main contrib non-free rpi
Jessieにアップデート
$ sudo apt-get update
$ sudo apt-get upgrade
$ sudo apt-get dist-upgrade
再起動後，Operating Systemを確認
$ hostnamectl
Static hostname: raspi3rd
Icon name: computer
Chassis: n/a
Machine ID: f64ca66647d24dd88e5251e391dbf582
Boot ID: 6303e40951a94ec092039f0cd64ae57b
Operating System: Raspbian GNU/Linux 8 (jessie)
Kernel: Linux 4.1.12-v7+
Architecture: arm
$
