How do I de-frac my lap top Windows Vista Basic.?

My computer is so slow and sometimes freezes up. It tells me, " high memory usage".

"High memory usage" means the internal Random Access Memory (RAM) is inadequate. It has nothing to do with your hard drive. The answer for that is to add more memory to the computer.

Defragmentation reorganizes the hard drive so all of the files are contiguous, saving the time the disk would take skipping over the surface to pick up file fragments.

To defrag a disk:

Start/Computer/Right Click the drive you want to defrag
Select Properties/Tools/Defragment Now/Defragment