vssadmin list shadowstorage - List ammount of shadow storage space
vssadmin resize shadowstorage /on=[drive letter]: /For=[drive letter]: /Maxsize=[maximum size]GB - Resize the shadow storage
vssadmin resize shadowstorage /on=C: /For=C: /Maxsize=15GB - Eg: Resize system restore space for drive C (using space on drive C) to 15GB.
