Hand histories are easy to find in the PokerStars client. First, click on Settings  over on the right side of the main lobby. Then look down the list on the left and click Playing History.  You will see two items appear, Hand History  and Tournament Summaries. 

To check the exact location of the saved hand histories, go to our desktop software and select 'Settings' ! 'Playing History' ! 'Hand History'. The folder you're currently using to save your hands will show just below 'Where To Save'.