To try this tips, we suggest to backup your hard drive data.
Mount your hard drive and launch Disk Utility. In the list of drives in the left pane, select the hard drive you want to partition (not the volume on the drive, but the drive itself). Click on the Partition tab that appears when you select the drive.
The Partition Layout area shows a graphic representation of your hard drive—initially it’s a single partition, partly outlined in blue (the blue indicates the portion of the drive that contains data, but not its location on the drive). Your first step is to resize this partition. You can do that by dragging up on the bottom right corner of this image (where you see three gray lines), or you can simply enter a new value in the Size field (700GB, for example).
Now click the plus-sign button (+) below the partition to add another partition. By default it occupies the remaining space on the drive (see “We’ve Got a Live One”). You can add more partitions if you like by clicking the plus-sign button again. To change their size, use the Size field.
When you’re ready to partition the drive, click the Apply button. (If you change your mind, click Revert to put things back the way they were.) Disk Utility goes about its business, making sure that your data remains on the first partition, as well as creating the additional partition.