A manual update from the User Interface is an incremental update, only the new/modified signatures.
Why you would need to do this is the question, as virus definitions are set to automatically download unless you have changed that setting - another issue if you have changed that setting from Auto you wouldn't get the streaming updates either.
However, you don't say if the above is the manual update you are going to do ?
There is a means of downloading the complete virus definitions database and that is everything and is quite large.
