your link to the update page should pass the ID of the record to be updated using a query string variable
you would create a recordset that uses the ID as a filter to return the correct record, then bind the initial value of the form elements to the corresponding column.
if you use the Data Assist wizard to create the search, results, update and details pages for you, this will already be in please, you can then add the insert button and insert behavior to the update page.