Not sure why you want to delete D: as it contains Windows 7 don't you want to keep Windows 7?
For you to delete any one of the partition that has Windows OS install in you need to first boot your computer to a Windows OS that you wont delete the partition for then type sysdm.cpl into Start Menu or Run box. From System Properties click Advanced and click "Settings" button at the Startup and Recovery section. Select the default operating system your computer boots to which is the operating system you have booted your computer with so if you want to delete Windows 7 select Windows 8. Type Msconfig into Start Menu or Run box. From System Configuration click "Boot" tab, select the operating system entry that you want to delete and click Delete button. Apply the changes. Open Disk Management by typing Diskmgmt.msc now you can delete the partition of the operating system install at make sure to backup file in that partition you will delete.
For you to delete any one of the partition that has Windows OS install in you need to first boot your computer to a Windows OS that you wont delete the partition for then type sysdm.cpl into Start Menu or Run box. From System Properties click Advanced and click "Settings" button at the Startup and Recovery section. Select the default operating system your computer boots to which is the operating system you have booted your computer with so if you want to delete Windows 7 select Windows 8. Type Msconfig into Start Menu or Run box. From System Configuration click "Boot" tab, select the operating system entry that you want to delete and click Delete button. Apply the changes. Open Disk Management by typing Diskmgmt.msc now you can delete the partition of the operating system install at make sure to backup file in that partition you will delete.