A Catholic is free—indeed, obliged—to reject teaching from any Pope that contradicts what has been taught from the beginning by all his predecessors.
Except that:
God has given the Holy Father a kind of infallibility distinct from the charism of doctrinal infallibility in the strict sense. He has so constructed and ordered the Church that those who follow the directives given to the entire kingdom of God on earth will never be brought into the position of ruining themselves spiritually through this obedience.
If Francis is giving teaching to the entire Kingdom of God that contradicts Catholic teaching and therefore brings about spiritual ruin (and requires Catholics to reject it and be disobedient), then Catholics need to question why God hasn't given the Church the aforementioned infallible safety with Francis at the helm.