help me please

hello

Help me please...
I have two "postgres" user. How to delete the first one ???

*******************
# select * from pg_shadow where usesysid=1;
usename | usesysid | usecreatedb | usesuper | usecatupd
| passwd | valuntil | useconfig
----------+----------+-------------+----------+-----------+-------------------------------------+----------+-----------
postgres | 1 | t | t | t
| | |
postgres | 1 | t | t | t |
md53532747417351142d5270721fcf740ed5 | infinity |
(2 rows)
*******************

*******************
# select * from pg_user where usesysid=1;
usename | usesysid | usecreatedb | usesuper | usecatupd | passwd |
valuntil | useconfig
----------+----------+-------------+----------+-----------+----------+----------+-----------
postgres | 1 | t | t | t | ********
| |
postgres | 1 | t | t | t | ******** |
infinity |
(2 rows)
*******************

I tried
delete from pg_shadow where passwd is null;

but it's not working.

Help me please
oleg