changing privleges in pg_user/shadow

hello all,

i am wondering if it is possible to change the attributes in pg_user and
pg_shadow for a paticular user. i can't seem to find any documentation on
'updating' users other than createuser and dropuser. is it possible to
change the users' attributes? for example could this doesn't seem to work:

mydb=>update pg_user set usecreatedb = 'f' where usename = 'mike';

the result is 0 records updated.

any help or pointers to some documention on this is greatly appreciated.

thanks
-mike

mike focosi
senior applications programmer
golden dome media
http://www.gdp.net
http://www.surfmichiana.com
http://www.wndu.com