The default save location of Documents, Music, Pictures, and Videos will be at C: drive in Windows 10, if not it was always at that location since the beginning of Windows. If you have a partition D: or something in your PC that is much larger in size and you would like to make that as the default location, it is quite an easy job and doesn’t need any serious modification or hacks – just a straight way change in settings.
Go to Action Center and click on All Settings.
Click Storage and choose the partition in each of the drop-drop list on documents, pictures, music, and videos. You will see that the New apps will save to: option can’t be changed. These are the apps that you install from Microsoft Store, they need to be installed in OS installed partition only.