This is simply a reminder saved as a wallpaper. 

To remove it you will need to change your desktop background (wallpaper). 

How to change your background on Windows 10

Select the Start Start symbol button, then select Settings  > Personalization  to choose a picture worthy of gracing your desktop background, and to change the accent color for Start, the taskbar, and other items. The preview window gives you a sneak peek of your changes as you make them.


In Background, select a picture or solid color, or create a slideshow of pictures.


          Desktop background personalization settings