comparing data in two tables

Hi I have on e table with id as primary key and insert idendity on and another bakup  table with same table structure. I would like to compare two tables on a button click event and make chnages to parent table based on back up table data. Means if there is a new data in parent table then delete data and if there is a missing data in parent table then insert data. How do I do that What is the best method?