Adjusting valves on a diesel motor can be pretty difficult. I would highly recommend taking this to your authorized dealer and having them adjust the valves on your diesel motor. There is just to much to risk to do it by yourself.
This is a fairly difficult repair. If you consider yourself a novice i would suggest consulting a licensed mechanic, or at the very least referring to the user manual that came with your car.
Go buy yourself a repair manual for your make/model vehicle & do it right the first time. There's no way anybody can honestly answer this question with the info. you gave.