I think what you are looking for is the function "unique". Try using:
B = unique(A,'rows')
That will delete repeated rows in matrix A, hence the parameter 'rows'. Regarding your second question, I don't think there's a function for that exactly but you can simply average both rows and store them in a new vector X. Then create a new matrix C using the new vector X and the rows you want from your original matrix A. If I wanted to delete for example the fourth row in your last matrix A I would do:
A = [A(1:3,:);A(5,:)]
Hope that helps.
