And What about the AppData folder where SIA wallet has taken up 8GB disc space? Can I change the default storage
Since you have Windows, I'll teach you
the trick.
You'll find out in your life that there are many apps that use AppData and such folders to deposit their data, since it's M$ standard and it has to be OK, right? And most don't have option to change that.
But you can make a symbolic link. The app will believe it uses a folder in AppData (or wherever...) and the actual data can be somewhere else, even a different drive.
You have to do (in AppData folder) something like: mklink /D your_unwanted_folder_name "D:\path\to\new\folder"
your_unwanted_folder_name has to not exist, you have to move it away first.