In your SQL statement there is no reference to the form in the right part of the assignement, so you replace OrderQuantity by OrderQuantity, i.e. you do nothing. Moreover, the references to the controls are inside the quotes, meaning that they are literal while the first condition makes no sense (if I understand correctly what you try to achieve):
"UPDATE table1 SET table1.orderQuantity = orderQuantity WHERE (((table1.orderQuantity)=forms!form1!text1) AND ((table1.orderDetailsID)=[forms]![form1]![List1]));"
It sould be something like:
"UPDATE table1 SET table1.orderQuantity = " & forms!form1!text1 & " WHERE (((table1.orderDetailsID)= " & [forms]![form1]![List1] & "));"