Important: Before continuing, be aware that deleting a partition will permanently erase all data from that drive. By all data I mean the operating system installed, all programs, all data saved by those programs, all music, all video, all documents, etc. that might be on that particular drive.
Highlight the partition you want to delete and then click the Delete link.
Note: Your list of partitions may differ considerably from mine shown above. On my computer, I am performing a clean install of Windows 7 on a computer with a single 30GB hard drive that has previously had Windows 7 installed.
If you have multiple hard drives and/or multiple partitions on those drive(s), take great care in confirming that you're deleting the correct partition(s). Many people, for example, have second hard drives or partitions that act as backup drives. That's certainly not a drive you want to be deleting.