Microsoft gave four news issues 4k quality, for them users of Windows 10. All topics are nature related.
The first issue is called At Home (in the home)
Read from the description of the theme: Enjoy the peaceful moments at home with these 15 premium, 4k images, available for free for Windows 10 themes. Download it here:
The second issue is Amazon Landscapes (Amazon landscapes)
Put on your desktop the waterways and forests of the most diverse area in the world with these 20 premium 4K images, free for Windows 10 themes.
Download Amazon Landscapes PREMIUM
The third issue Amazon Wildlife (Wildlife of the Amazon)
The tropical Forest the Amazon has more species of animals than anywhere else in the world. Check out 18 of these premium 4k images free for Windows 10 themes.
Download Amazon Wildlife PREMIUM
There is also a new regular theme (not 4K) for Windows 10. Reclaimed by Nature (Recovery from Nature)
Scary or wonderful? These 16 images of vehicles and architectural buildings recovered from nature are free for Windows 10 Themes.
If you have a lot of themes installed and you no longer need them, you can delete them.