I’m using the latest free version of Unity, and according to the docs:
To use the Sprite Editor, you will first need to ensure that your sprite texture has the Sprite Mode set to Manual in the texture importer (and also remember to click the Apply button after the change). When you do this, a button to open the Sprite Editor will appear in the inspector. You can also open the editor by selecting a sprite texture from the Project panel and selecting Window > Sprite Editor from the menu.
However, I don’t have “Sprite” option when selecting texture type. Is that a Pro feature?