How remove the file which was created by another user?

When I try to remove the file which was created by another user through super user, I am getting the "override protection 644 " meesage.

Could you please anyone help me how will I delete the file without prmpting the override protection.

I have also given the permission (rwx) to the group as well.

Ex : -

$pwd
/root/mydir/kandir/
$ ls -ltr | grep '^d'
drwxrwxr-x   2 kandir   staff         96 Mar 22 02:37 mydir
$
$cd mydir
$ pwd
/root/mydir/kandir/mydir
$
$ ls -ltr
total 16
-rw-r--r--   1 kandir   staff          3 Mar 22 02:37 hi.txt
$ su - reddy
Password:
$ pwd
/root/mydir/reddy
$
$ cd /root/mydir/kandir/mydir
$
$ pwd
/root/mydir/kandir/mydir
$
$ rm hi.txt
rm: hi.txt: override protection 644 (yes/no)? ^C
$
$
$

rm -f hi.txt

it is not removed through super user as well....Can any one please help me how to remove the file with the above scenario

Is "reddy" in the staff group like "kandir" is ? If so, "rm -f" should just work. Make sure you "rm" is the real command and not some broken alias like "rm -i" like Gnu/Linux does.
Try "/bin/rm -f" if you are unsure.