Transfering EVERYTHING to new HDD

I have a 40GB HDD that came with my computer, and my new(er) 250GB slaved to it. I have decided i want to move everything to the 250 so i can take out the 40. How can i do this, and i mean i want everything, all files, the OS, programs, everything. A step-by-step would be nice, but any information will help. Basically, i want the 250 to take over as the main HDD, thaks.