Hello, this is Emily.
Where do you see the 512 GB of data?
Can you type sysdm.cpl in the search on the taskbar and hit enter, go to Advanced tab, click on the "Settings" button at the User Profile section. Now in the pop up, do you see other user profile other than your own and the Default one? If these other user profiles are for users no longer using this computer, you can safely delete them here in this pop up window to free the storage. Just make sure you don't delete your own, and you don't delete the "default" one either.