help me plz with 2 postgres users

Hello?
help me plz? i don't khow what to do...

How can I delete first postgres user.

template1=# select usename,passwd,valuntil,ctid,xmin,xmax,cmin,cmax from
pg_shadow where usesysid=1;
usename  |               passwd                | valuntil | ctid  | xmin
|   xmax   |   cmin   | cmax
----------+-------------------------------------+----------+-------+------+----------+----------+------

postgres |                                     |          | (0,1) |    1
| 16754522 | 16754522 |    0
postgres | md65476547442532.. | infinity | (0,2) |    2 |        0
|        0        |    0
(2 rows)

thx for your help.
Oleg