What is the point at which promotion occurs? Does the pawn as it enters the 8th rank become a promoted piece as it enters or does it have to occupy as a pawn then be promoted? If promotion occurs as it enters then a pawn would not be blocked from moving to the 8th rank if some piece was in its way.
When a pawn reaches the 8th rank, it then must be promoted to a Queen, Rook, Bishop or Knight. The pawn can capture normally to reach the 8th rank. IE fxg8=Q, but as we know the pawns don't attack pieces whom are directly blocking them so captures straight is not an option.
According the the FIDE 2017 handbook promotions can be done in numerous ways: 4.6.1 the pawn does not have to be placed on the square of arrival, 4.6.2 removing the pawn and putting the new piece on the square of promotion may occur in any order. 4.6.3 If an opponent’s piece stands on the square of promotion, it must be captured. It is worth noting that incorrectly promoting in Blitz or Rapid games results in a loss by illegal move according to the official rules.