Architecture :: How To Handle Multiple Users Changing Same Data

I have a form which allows users to modify data, what's the best way to handle that so if two or more users try to make an update i get the data in there properly without overriding the new stuff. for example if name and bday are in the form, user1 changes name but not bday, same time user2 accesses the form, the original name and bday are there, user1 saves, but when user2 saves, since he had the original name value the original is saved over the first.