There are 5 different difficulties in the Classic (Training, Easy, Moderate, Advance and Expert) and 4 in the Lightning (Gentle, Easy, Moderate, Intense). You''ll need to complete 9 total puzzles.
To cheat, visit
http://www.sudoku-solutions.com/, type in the numbers you are given, then click on "solve" and the site displays your answers. Input them into your game and your done.
Just a little pointer, you'll have to scroll down in the Classic game mode to find the Expert difficulty.