After a screen asking about additional software, you will asked what you would like to do with your hard disk.

If the installer refers to any sort of dual-booting, you must quit the installer and make unallocated space on your hard disk somehow. (See warning for info.)

If you are experienced with partitions, you may use this partition editor.

If you decide to use the partition editor, please be very careful. Partitions made with this partition editor can cause any other operating systems to become inaccessible.