Which disk drive? The floppy, CDROM, or the HDD? If it is the CD ROM or Floppy, there is a little switch or lever that will pop it right out. You can then pop in a new one.
If it is the HDD, there is a little more too it, but by no means difficult. You just have to find out where your hard drive is. There is usually only one screw holding in the drive bay. Take off that screw, lift up in the panel to unlock it, and then slide the bay out. If you need it more detailed, just tell me.
Quite easy to do. If you have someone else do it, it's going to cost you at least $50. Basically paying someone $1500 an hour to change your hdd. Save the money, and do the two minute job yourself.