Sorry but if you do read this, please help me if you are a mac user...

My Laptop wouldn't let me watch videos because it said i needed to download Adobe flash player

so i went ahead and downloaded it, but when i tried to download it, this came up.

The thing with my Laptop is that..

I bought it off someone on Amazon and they never told me the Name and Password

so i cannot download Flash player which is really annoying for me, considering i do alot of embedding and downloading required for some of the things i do.. 

How can i retrieve all that information again?
Since it was a seller on Amazon there's not really a way to get in contact with the seller again

I sent him an email regarding this but he never replied and doesn't look like he will anytime soon..

I once tried to change my name and password and after numerous hours of research

i got to the place where i could change it but it required my old password in order to change it to the one i want....

how can i change my username and password

or retrieve that old information..?