Updating a row in the database

What's the difference between updating an entry in the database using
the #save method and the #update method?

Thanks,
Thomaz

A save made a check for see if the Object exist or not. If exist, the
Object is save else, it's update.

With the #update, you must use a id who exist and define the attribute
to update. And it's a public classe Method not instance method, so you
use it only with Name class, not with your Object.

I'm coding a change password method in my application. When I use
#update, a invalid password gets saved. The same doesn't happens with
#save.

How use you update method ?