How to change default app for downloaded photos

[mizdaq]

Hi all,

New owner of an Acer Iconia running Android Marshmallow (5.1)

When I'm sent a photo and download it, it automatically goes to the Acer Gallery app (which I don't like). I want it to go to Google Photos app instead. I cannot figure out how to do so. I've already tried Settings>Apps>Gallery/Google Photos and tried to Clear Defaults but with both apps, there are no dafaults set, so the option is grayed out.

Would love to solve this problem, and also uninstall the Acer Gallery app altogether if possible.

Thanks!