You cant just change to a bigger hard drive.
EVERYTHING your computer has in it and does including how to turn on is on that hard drive.
What I did with mine is just add another one and turn it on.
Move all the stuff you want to save ontu the new hard drive and leave the operating system on the old one.
I have been told that the drive that crashes most often is the one with the OS on it.
that way all the important stuff will survive.
If you download music or pictures change the destination folder to the new drive.