How to make a reference type from int

i tried:

int i = 5;
object o1 = i; // boxing the i into object (so it should be a reference type)
object o2 = o1; // set object reference o2 to o1 (so o1 and o2 point to same place at the heap)

o2 = 8; // put 8 to at the place at the heap where o2 points

after running this code, value in o1 is still 5, but i expected 8.

Am I missing something?