MySQL REPLACE error?

I've never really used MySQL before, but considering I'm using it for a Counter-Strike: Source plugin, I'm trying my hand at it. I need it to replace the row with new values, if the row exists, and if it doesn't it creates it. Replace, from what I've been told, does this.

However, it decides that it's going to create an entirely new row, instead of replacing the existing one.

This is what I'm using:

</p><p>REPLACE INTO `users` VALUES ('STEAM_0:1:25175244', 'Hunter S. Thompson', '1', '26000', '1')

Does anyone know how to do what I'm looking for?

Thanks.

UPDATE users SET steam = 'STEAM_0:1:25175244', name = 'Hunter S. Thompson', etc WHERE id = id

edit by your needs, replace is not that you need here :P