updated OS to 10.6.8, can't figure out how to restore from time machine

So I took my 2007 macbook to the apple store(service center) today in India and got my OS updated from 10.5 to 10.6.8.
The guy at the place was being iffy about restoring everything from my back-up via time machine (on my external hard drive) so I told him i'd take care of it.
I came home and started my laptop and it's running just fine but i cannot for the life of me figure out how to do this restoration. I have a hitachi 500gb external hard drive which has the most latest back-up from last night. When I plug in the external to my laptop, it's reading it and everything. Now i just need someone to help me by telling me how i can restore everything.

In January while I still lived in Arizona, I had gotten my hard disk replaced and the guys at the genius bar had restored everything from my external hard drive and when i opened my laptop at home, everything look exactly the same as it did before they changed the hard drive.
Now that i've updated my OS, i would like my laptop to look like it did last night when i backed it up.

Please help!