How can I reset the main password?

Hello can someone help me? I am living in France and I needed to get my MacBook Pro repaired. When I got it back, my password would not work, I went back to the store, I was advised to to use the main password and reset my password. I don't remember the main password, having not use it in a long time. I was then told to use the disk that came with the laptop and reset the main password. My problem is that the disk is in the US and I am in France where I will be for 6 months. What can I do to be able to open my laptop. I would appreciate any help. Thank you