How can you modify an existing sketch in Autodesk Inventor?

Modifying an existing sketch in Autodesk Inventor is primarily done by entering the sketch environment. Within this environment, users have access to various editing tools and commands that allow for precise adjustments. For example, you can modify dimensions directly by selecting the existing dimension and inputting a new value, or you can edit geometric constraints that define the relationships between sketch entities. These functions provide the essential means to alter the characteristics of your sketch to fit design requirements.

The other options do not provide a method for modifying a sketch. Exporting as an image merely saves a visual representation of the sketch without allowing for alterations to the actual geometry. Applying shading and colors pertains to presentation and visualization rather than enabling changes to the sketch's structure. Converting a sketch to a 3D model involves a different process, meaning that it's not directly modifying the sketch itself but rather using it as a basis to create a new feature. Therefore, accessing the sketch environment and utilizing the available editing features is the most effective way to make modifications.