As to how? Pretty irrelevant as there is no way to replace it in a 50-50 country, but I would think 3/4 of the states approving it would suffice. Would probably have to be drawn up by a convention, not by Congress.
I think it would be virtually impossible to even come up with a proposed new Constitution.
For example -:
the Pro-life would demand a article saying conception makes a new person
The Pro-abortions would demand an article allowing for abortion - and then there would be disparagement as to the cutoff - ie - 3 months, 6 months, 8 months - 9 months, 3 months after birth
The second amendment -boy o boy
10th amercement - to what extant
The electoral college - another O-boy
Citizenship - vs illegal aliens - another O-boy
Voting rights - should it be uniform at least for federal elections
only citizens? age, is voting a right? should all voting be in person
(other than valid reasons - should there be a national voting ID?
Term limits? POTUS - remain at 2 terms - should a term be 4 years or 6 years
what term limits and term length for congress - House remain at 2 years?
How many months should be considered a full term - ie POUTS is 48 months -
should 24 months be considered a full term or 30 or 36 months?
How should the pay of congress be considered?
Should committee leaders be given extra pay
Should majority/minority leaders be given extra pay
How to brings new states/commonwealths be brought into the Union
Should a State/Commonwealth be allowed to leave at will?
if so - what about Federal facilities -ie military, other Federal offices, ect
Should DC become a State? if not should they have representation in Congress?
The original constitution called for 1 rep for each 30,000. Using that formula - we would now have 11,000 Rep. How should a good representative be counted? Should a State/commonwealth be limited to a maxium number of Rep? ie say Calif is entitled to 60 based on population - but lets say no state will have more tha-n - say 50 reps
Should there be two Veeps - the second one would be the President of the House of Rep
Age limit for elected officials
Age limit for judges?
Should the USA form a new govt - which would negate any - previous treaty
if so - what about treaties with the Indians?
other issues......
FWIW - when the Constitution of the CSA - was written - much of it was word for word of the USA