Update and select in one query

You can't.

There's no convention in a SQL UPDATE statement for returning data. And vice versa -- a SELECT statement doesn't write information to a table.

If you've found questions/answers that you feel are similar to what you want, please provide links.

UPDATE tblPopUp  
SET PopUp = 'False', Period = Period  
OUTPUT DELETED.Period
WHERE DisplayNo = 1

For more information about OUTPUT clause please check this post.