const n=6;
var a:array[1..n,1..n] of integer;
i,j,s,c:integer;
begin
Randomize;
for i:=1 to n do begin
 for j:=1 to n do begin
 a[i,j]:=random(17)-10;
 write(a[i,j]:5);
 end;
writeln;
end;
writeln('По столбцам:');
for j:=1 to n do begin
 for i:=1 to n do write(a[i,j]:5);
 writeln;
end;
s:=0;
for i:=2 to n do
 for j:=1 to i-1 do
  if a[i,j]>0 then s:=s+a[i,j]; 
writeln('s = ',s);
 for j:=1 to n do begin
  c:=a[1,j]; a[1,j]:=a[n,j]; a[n,j]:=c;
  end;
for i:=1 to n do
 begin
  for j:=1 to n do write(a[i,j]:5);
  writeln;
 end;
end.

Пример работы программы:
   -9    2  -10    4    3   -2
  -10    3    4    5   -4   -9
   -3   -4    4   -4    5    2
    1   -1    3   -9    5   -3
   -8    4   -4    6   -2   -5
    5   -2   -4   -4    2   -1
По столбцам:
   -9  -10   -3    1   -8    5
    2    3   -4   -1    4   -2
  -10    4    4    3   -4   -4
    4    5   -4   -9    6   -4
    3   -4    5    5   -2    2
   -2   -9    2   -3   -5   -1
s = 21
    5   -2   -4   -4    2   -1
  -10    3    4    5   -4   -9
   -3   -4    4   -4    5    2
    1   -1    3   -9    5   -3
   -8    4   -4    6   -2   -5
   -9    2  -10    4    3   -2