Update Instock

[firsttime]

Hi,
I have a form that displays an updated stock level for each product ID. The form is a Continuous form so
it displays more than one record. I need to change the InStock value in the table with the new values from the text1 field on the form.

Example: I have a form that contains 2 table. 'Products' table in the mainform and 'order details' in the subform(like Northwind). In the mainform i have a field Instock,a Unitorder field and a text1 field. In my subform i have a field quantity.

Formula:
text1=[unitorder]+[subform order detail quantity].
Instock=Instock(default value=0). Formula works!!

If i put the formula in Instock, it works too. But it just show the new value in the form and don't update it in the table (Instock is still 0). So i made a text1 field in the form with the formula in it. But i don't know how to update the value in text1 to Instock(in the table).
I hope that i explained it better now.

Is it possible to change/update a value from a field in a TABLE with a value from a field in a FORM with a code????

I hope that you guys can help me,

THX IN ADVANCE

Dan