Windows 10 is shipped with a new photo viewer app called Photos, which is also the default app for managing photos and pictures on the new OS. However, if you'd like to use another program (such as Paint or Windows Photo Viewer) to manage your photos, this tip will explain two simple methods for changing Windows 10's default photo viewer.
Change the Default Program for Photos in Windows 10
Change the Default Photo Viewer in Windows 10
Click on Start and go to Settings > System > Default apps. Click on the Photo Viewer dropdown menu and select the app you'd like to use:
The new setting will apply to most if not all image file formats (.jpeg, .png, .gif…).
Change the Default Program Association for a File Type
Windows 10 also enables you to change the default program for opening a specific file type. For example, if you'd like to automatically open PNG files in Paint, you simply need to change the default program association for the selected file type (.png).
Open your Pictures library, right-click on any PNG file and select Open With > Choose another app:
A menu that reads,"How do you want to open this file" will appear. Select Paint from the list of proposed apps and tick the Always use this app to open .png files checkbox: