Please start new threads for new questions so that others that have the same question can find it more easily in the future on the forum.
To fix your problem, open the server behaviors for each upload and set the "Default Value" for each to come from the existing value from the recordset on the update page.
That will force it to maintain the old value when no value is entered. The Default Value is used when the field is blank and it is set to the current value in the database.... just make sure the update recordset is above the upload code.