Bank One is the passenger side, Bank Two is the drivers side. (Bank One, Sensor One = before cat, Bank One, Sensor two = after cat. Bank Two, Sensor 3 = before cat, Bank Two, Sensor 4 = after cat). It looks like those two codes are telling you that both sides/banks are seeing lean conditions, so it's doubtful that O2 sensors on both banks would go bad at the same time, but stranger things have happened I guess.

They basically thread into bosses on the exhaust pipes, so removal and installation are relatively simple using an open-end wrench. The only specific requirement during installation is the use of O2 specific anti-seize for ease of future removal.

While it doesn't necessarily narrow things down much, other possible causes could be vacuum related issues with the intake manifold , the pcv valve, and/or the egr valve.