Photo Viewer is a free Microsoft program that comes with Microsoft Windows. If you're running Windows 7, 8 or 8.1, it's the default program for viewing photos on the operating system. You can search for any new Windows Photo Viewer update using the Windows update tool. In Windows 10, they've largely replaced Photo Viewer with a tool called Microsoft Photos, though you can still use Photo Viewer if you wish.
Finding a Photo Viewer Update
Windows Photo Viewer comes with Microsoft Windows versions 7 and up, but Microsoft may introduce updates to the software over time. If you want to see if there's a Photo Viewer update you can install, you can use the Windows Update tool to search for one.
Press the Windows key on your keyboard, then type "Update" in the search box and press the enter key. Click the Windows Update icon, then click "Check for Updates." If you see a Photo Viewer icon appear after Windows is done searching for updates, check the checkbox next to it. Then, click "Install Updates" to install the updates to Photo Viewer. If you're prompted to restart your computer, save any work and close any open programs, then click "Restart."
Once your computer restarts itself, the Photo Viewer update should be available for use.
Microsoft Photos and Photo Viewer
In Windows 10, Photo Viewer has been mostly replaced with a new app called Microsoft Photos. If you're using an older version of Windows, Microsoft Photos will be installed if you install Windows 10. You can find the latest version of Microsoft Photos for free in the Microsoft Windows online store.
You can continue to use Photo Viewer under Windows 10 if you choose to do so. This is easier to do if you installed Windows 10 on top of a previous version.
In that case, you can set it as your default photo app using the Windows 10 Settings menu. Click the "Start Menu" and type "Settings" in the search box, then click the "Settings" icon. Within the "Settings" menu, click "System" and then click "Default Apps." Under "Photo Viewer" choose the app "Windows Photo Viewer" and then exit the menu. Photos will be opened using Windows Photo Viewer in the future.
If you're using a computer that came with Windows 10, you'll have to edit the Windows registry, a database of operating system settings, to enable Photo Viewer. You can find files online to do this, but make sure you trust the source of any registry changes you make since they can harm your computer.