Mid-November 2015, Google changed Google+, and one of the things that changed was how you update your banner image. The first thing you’ll need to do is log into your Google+ business page, and you’ll notice the icon up here in the upper right-hand corner. This way, you know you’re on the right page.
Now, on the left-hand side, all you need to do is click on “profile”. Here, you’ll see your current banner image, and you want to click on the “edit profile” button. Here, you can update your profile image or your banner image. All you need to do is click on the photo icon. You can choose a photo that you’ve already uploaded, or you can upload a current photo.
For me, I’m going to update the photo for a holiday photo, and I just want to make sure I grab my Google+, because it is a specific size. Once you’re done, click “done” here, and then “save” in the bottom right-hand corner. And this will update your banner image.