If you want to edit the boot setup, or partitions...

Then before you start, get these two programs. Both are free, and both are quite useful if you want to look at or change your boot sector, or modify your hard-drive's partitions by changing their sizes, or creating another partition, or wiping or formatting a partition, or just verifying what's on where. The above shows my dual-boot setup for Windows 8.1 and Windows 7.