You can download a free trial of
Wipe Drive , or you can download
Active Kill Disk. Either of these will wipe the drive.
Most manufacturers of hdds have software for partitioning the hdd, if you go to the web site of the manufacturer of your hdd you should be able to find this. Or you can tell us what make and model you have and we can look for it for you.
Most BIOS have a limit of 137GB that they will recognize and this could be why you don't see the rest of your hdds space. There are a couple of ways to get around this so that you can use the whole drive, the simplest is to make partitions smaller than the 137GB limit. If you make two partitions and place the OS on one and your files on the other you will have the advantage of being able to reinstall you OS if necessary without effecting you files.