I’ve just spent half the day trying to fix the address of one of my Raspberry Pis. No matter what I did, it kept the address that it was assigned some time ago.
I even tied the IP address to MAC in the router – and THAT didn’t help. Countless resets of the router and the board got me nowhere until I read this:
My /etc/network/interfaces file didn’t look like that so I updated it… turns out in Jessie you have to update the file /etc/dhcpcd.conf
Even getting this far, some tutorials said you needed far more information than this or the Pi would not be able to contact the outside world. Well, mine does now and the address fixing works. Worth keeping that link in your bookmarks.