IIRC, pretty much everything about the courts is in Article Three of the Constitution. Article Three:
-Establishes the Supreme Court (but no specific positions or requirements for number of justices, though the office of Chief Justice is established in Article One),
-Gives the Supreme Court original jurisdiction in a few areas. It gives appellate jurisdiction to all other "
cases and controversies" arising from federal laws/treaties/etc, but that jurisdiction is subject to the laws passed by Congress.
-Requires judges to be paid and establishes that they serve lifetime appointments,
-Empowers Congress to establish inferior courts
Additionally, Article 2 establishes that the president appoints Supreme Court justices with the advice and consent of the Senate.
So any kind of term limits, or a change to how Supreme Court justices are appointed, would require a constitutional amendment. But Congress could theoretically, for example, abolish all courts except the Supreme Court and establish new courts, expand the size of the Supreme Court to 100 judges, or strip the Supreme Court of its appellate jurisdiction.
