You cannot delete an element inside the array.
Even if you set it to NULL, it still exists.
The only thing you can do is decrease the size of the array.
SQL>
SQL> declare
2 type month_va is varray(13) of VARCHAR2(20);
3 v_month_va month_va:=month_va();
4 v_count_nr number;
5 begin
6 v_month_va.extend(3);
7 v_month_va(1):='January';
8 v_month_va(2):='February';
9 v_month_va(3):='March';
10
11 v_month_va(2):=null;
12 if v_month_va.exists(2)
13 then
14 DBMS_OUTPUT.put_line('Object Exists');
15 end if;
16
17 v_month_va(3):=v_month_va(2);
18 v_month_va.trim(1);
19 DBMS_OUTPUT.put_line('Count:'||v_month_va.count);
20 DBMS_OUTPUT.put_line('Last:'||v_month_va.last);
21 end;
22 /
Object Exists
Count:2
Last:2
PL/SQL procedure successfully completed.
SQL>