how to replace the element in matrix?

i have a matrix

if true
  A = [ 1 5 9 7
        3 5 7 8
        8 2 4 6 ];
end
now i want to put number 12 in the location of A(2,2)
also i want to put number 13 in the location of A(3,3)
how can i do please help me

Answer 1

[Yao Li]

A(2,2)=12;
A(3,3)=13;

[deniz yükçeken]

how can i do it with a column

[Burak Ahmet Celebi]

A(:,2)=12;

A(:,3)=13;

A = [ 1 12 13 7

3 12 13 8

8 12 13 6 ];