Hi, I'm having problems with my Fiesta with a lack of power and the engine management light turning on and off!!

I took my car to a friend with a diagnostics kit and it showed the following codes:

HO2S-11 (Heated Exhaust Oxygen Sensor Right Upstream) Circuit Slow Response
System Too Lean Bank 1
HO2S-11 (Heated Exhaust Oxygen Sensor Right Upstream) Circuit Malfunction
Invalid fuel tank level message from instrument cluster
Knock sensor 1 circuit malfunction
HO2S-11 (Heated Exhaust Oxygen Sensor Right Upstream) Circuit Slow Response

I changed the Oxygen sensor back in 2014 - Could this have gone already?

I would be extremely grateful for any advice anyone may have for me!!