Why has the US Federal Reserve raised interest rates?

It looks like Donald Trump's pick to head the US federal reserve isn't following orders. The man hand-selected by the US President has decided to do the exact opposite of what Mr Trump has been asking. Chairman Kevin Warsh has announced an interest rate hike for the world's largest economy. The President is not happy and has reiterated his calls for interest rates to be lowered. So why has the Fed made a very different decision?