Steps to change the wallpaper of your pc-

i.) Go to settings and click on the personalization option.

ii.) You can choose default backgrounds or browse a background from your pc.

iii.) To browse a background click on the browse option.

iv.) Choose a picture from your computer and click on the choose picture option.

v.) For more information check out this video: https://youtu.be/TNxq6NpCQhw