Here is an example code that would help:
A = [22 33 43 55;
11 22 -33 44;
55 22 33 -44;
99 88 77 66];
[row_neg col_neg] = find(A<0);
A(row_neg,:) = [];
This should manipulate A to
A =
22 33 43 55
99 88 77 66
