Pareto optimum in game matrix I have to find Pareto optimum squares in game matrix. They are marked in following picture 
What questions do I have to ask myself for every square to decide if it is Pareto optimum?
Why square E/A (5,4) is not optimal?


Pareto optimality is a state of allocation of resources in which it is impossible to make any one individual better off without making at least one individual worse off.

E&A with a value $(5,4)$ can be improved to F&D with a value of $(5,5)$ since the second player is better off and the first player is not worse off.
Similarly F&A can be Pareto improved to F&B or F&D or G&D, and you can find examples of improvement without worsening for all the cases without red rings, but you cannot for any of the cases with red rings.  
