How do I remove a doorknob to tighten the screws?

I have a doorknob that is coming loose. All I need to do is remove the doorknob to tighten the screws, but I can't remove the doorknob. The screws are hidden under the rose (?), and there are 3 small holes on the doorknob, but no latch to push in. I have tried sticking pins into the three small holes to pry the doorknob off, but nothing is happening. Please help.