Instructions
PC
Click the "Options" button from the main menu of the game and then click "Controls."
Click the button assigned to an action and then press the key on your keyboard that you want to reassign to the action. For example, to change the key to open your inventory from "E" to "I," click the button next to "Inventory" on the controls screen and then press the "I" button on your keyboard.
Click the "Done" button once you are satisfied with the way that you have set up the controls.
Click the "Invert Mouse: OFF" button on the options screen to change the setting to "ON" and play with inverted camera controls. This means that instead of pushing forward on the mouse to look up and back to look down, you have to do the opposite, as though the mouse were a joystick guiding the nose of a plane.
Click "Done" to save the changes and return to the main menu.
Xbox 360
Use the left analog stick or directional pad to highlight "Help & Options" from the main menu and press the "A" button.
Highlight "Controls" and press the "A" button to view the presets.
Use the left analog stick or directional pad to scroll through the three preset control layouts and press the "A" button to select the one most suited to your playing style.
Highlight "Invert Look" and press the "A" button to reverse the look controls.
Highlight "Southpaw" and press the "A" button if you are a left-handed player and want to swap the controls mapped to the analog sticks. With this mode enabled, you use the right analog stick to move around and the left analog stick to view your surroundings.
Press the "B" button once you are satisfied with the changes.