Okko Era of Asagiri - Maximum Heap Size too large

I am completely new to this and the first thing I’ve tried to play has come up with a warning box saying the maximum heap size is too large and I should lower it in my preferences. Where exactly do I need to be going and lowering this heap size?

The maximum heap size is set on the General tab of the Preference dialog, which you can bring up via the File menu, after loading the module.

To what do you have the maximum heap set now?