Don't take a Smith & Wesson revolver apart UNLESS you truly understand the mechanism. The problem you're having is a common one. Most of the time it's caused by simply not pushing the cylinder latch far enough forward with your thumb. Because this is a part that often has to wear-in I'd leave it alone for now. If the problem persists give Smith a call and seek their help. (If you bought the gun new, it might very well cost you nothing but time.)
'Wisdom To One Is Foolishness To Another; But, Alas, A Fool Knows Not The Difference; And, The Road To Hell? ...... It Remains Well Trod By Those Who Should Know Better.'