If a person in Hell repents and believes in God can that person enter Heaven?

No a person cannot leave Hell once they are there.  Belief in God is not going to be a problem for those in Hell, and eventually the lake of fire, because they are going to see and stand before God on the Day of Judgment.  They will know that He exists.  And mere belief in God is not enough anyway, the devils also believe in God and they tremble because of it (James 2:19).  The choice has to be made while the person is living on this earth; to either accept the saving work of Jesus Christ to pay for their sins or to reject it and pay for their sins themselves.  There is no escaping Hell and getting to go to Heaven; once a person is there they are there until the Great White Throne Judgment, then they will be cast into the lake of fire.