Once you've made all the photo edits you'd like, you can save and share your photo. Click on the Save button on the upper right corner of the screen. You'll be asked to save or discard changes, as usual, but you'll also be asked if you'd like to replace your existing photo or save a new copy. If you replace your photo, it's going to overwrite the existing photo. In my case, that's just fine. The existing photo wasn't going to be used for anything, so I'm saving myself the trouble of having to delete it, anyway. In other cases, you may also want to use the photo for other purposes.
You may see an image of turning gears as all of this processes. Google+ has very fast photo processing by Internet standards, but it's still sometimes pretty slow for someone used to editing on more powerful photo editors.
Once your changes are applied, you'll see the same photo details view as you did in step two. To share your photo on Google+, simply press the Share button on the lower left side of this screen. Your photo will be attached to a message you can share with the circles of your choice or the public in general. Once you share the photo, the viewing permissions for the photo will also be changed.
If you really like your photo, you can also download it from the details view. Select Options from the right bottom corner of the screen, and then select Download Photo. Enjoy!