Hello,
If the requirements to play the game on Mac is 4GB of RAM (or memory), that is the minimum required and I would not recommend playing with anything lower. Unfortunately, I have seen many issues where people did not meet this requirement and the game was unplayable.
I think you may be confusing RAM with hard drive free space - they are not the same. The game requires 4GB of RAM (you have 2GB) and at least 10GB of free space on your hard drive. Unless you upgrade and add more RAM (this costs money), you will not be able to play the game on your Mac.
I hope this helps and keep simming,
Cody