Clearing your choices:

Click next, then previous, the current step will be reset.

Drawing a custom shape (SmartCart) :

First, indicate the width between the legs of the cart, relative to the entire width, and click once to confirm their position.
To draw a line, click at the endpoint. To draw a curve, click at the endpoint and then drag to define the curve.

Dialog boxes:

Follow instructions at the top of the pop up windows and select from available values. If the window says that you may not use some option, either go back to change your configuration or click next to continue as it is.