After the render is complete go to file / save image as or Export Image. And save it to your hard drive. Another tip is to go to edit / Preference, the enable ( Image with scene open/save ) Then every time you save a project file the render will be saved with it. This is real handy because you can stop a render before it's complete save then at a latter time open the project back up and use the resume render button to pick up the rendering right where it left off.

Stephen Ray