Update only filled records from User Form to table in access 2007

Hi,

I have built a data entry form in Access 2007. Half side of user form is for New Data entry & half side is for update existing records. I'am adding New data entry record in table via command button using INSERT INTO statement.

In update existing records side of user form i have built 7-8 text boxes for selective fields, which generally gets updated from customer side by giving written request to my company. Sometimes customer gives request to update all at once & sometimes only 1 or 2 fields.

I want to update only those fields by pressing command button in my table which are filled in user form. Rest one should remain same in table as they were earlier.

I have tried searching many things on various sites in last 2-3 days but didn't get anything.

Appreciate if someone can help me in this part...this one is really urgent as i have to present this to my senior in next 3 days.

A Very Big Thanks in advance...