hi there. i'm quite new to macs, as this is my 1st one. basically i need to get more space on my laptop and i want to get rid of the rubbish i no longer need. i've gotten to the disk utility bit. on the left it shows my hard drive saying it is 183.GB toshiba and below it it says Macintosh HD. can i format this so i have more space on the hard drive of the computer?