Can the total number of members change in Senate?
No, it could not be changed by Congress alone. The US
Constitution would have to be amended to do so. According to
Article V of the US Constitution, the process would take a vote of
two thirds of both houses of Congress to propose such an amendment,
or upon an application by the legislatures of two thirds of the
states, it could call for a constitutional convention for the
proposal of such an amendment. Once final form of the amendment has
been settled upon, it would have to be ratified by three quarters
of the States, in order to make such a change to the Constitution.
This would result in an Amendment to the Constitution (similar to
other amendments, such as the 19th Amendment, which gave women the
right to vote).