This article explains how to remap Grid Controller's key bindings. The default key bindings are just my personal preference, but they're easy to change.
If you're using Unity's built-in input manager -- aka "Input Manager (Old)" in Player Settings -- edit the inputs in Project Settings > Input Manager:
If you're using Unity's Input System package -- aka "Input System Package (New)" in Player Settings -- edit the GridControllerInputActions asset located in Plugins > Pixel Crushers > Grid Controller > Prefabs > Input System:
If you're using Rewired, edit the actions in Plugins > Pixel Crushers > Grid Controller > Prefabs > Rewired > GridControllerRewiredInputManager in the Rewired Input Manager editor window.