I am following some instructions from internet.
Now I am at the hard drive. But how do I disconnect those cables especially hard drive data
cable. It seem like the hardest part. Removing RAM is easy.
The cables on HD have no handles/grip

For the power cable, wedge a flat-blade screw driver in between one of the sides of the power cable and the socket it plugs into, and use it as leverage to pry it out at an angle - they're sometimes in there real good. The data ATA cable will simply come out if tugged at with some force.

Thanks, that worked!