Sensor cleaning

I found a few spots on my D800 (approx 1500 shots), the lens is clean and I have tried the menu option for cleaning the sensor with no change so I assume this is oil on the sensor and want to clean it or get it cleaned however, I have absolutely no experience cleaning sensors myself and would appreciate any advice...

Is it easy for a first timer or is this something I should not attempt?
Recommended products to use?
Procedure to clean the sensor?

Thank You

Don