% Example matrix A
A=[1,2,3;4,5,6;7,8,9]
1 2 3
4 5 6
7 8 9
% define index of upper elements , triu: all above K=1 diagonal
idx = logical(triu(ones(size(A)), 1))
0 1 1
0 0 1
0 0 0
% extract as vector
v = A(idx)'
2 3 6
% convert back as matrix, if required
B=zeros(size(A));
B(idx)=v
0 2 3
0 0 6
0 0 0