How to delete ALL MY HISTORY!??!?

okay so my laptop has ALOT of privet stuff and my mom and dad are very suspicious and always know what im up to by seeing my history and my mom is going on vacation and she wants my laptop she sas she wants to "fix it" when honestly she wants to look at all my history its really privet what do i do and when i delete all my history is their a way of them still seeing my history by going to best buy and asking them please help =(