Simply complete all 16 Matches in the Single player career mode.
My personal tip is to go all in either straight away or after the flop. Hopefully you'll end up vs 1 or 2 people, you can then use the "x-ray cheat" to see their cards to see if you win and adjust the game accordingly.
On the be the richest after x amount of hands challenges, just get a big win early on and fold for the rest of the game. You can still use the steal cheat to for good measure.
To defeat the Robot in the last challenge just go all in straight away and use the x-ray cheat ( it will be hard to pull off, but if you fail just restart it ) and you should be able to win easily.