Merging or Extending Drives in Windows 8

To merge Windows 8 Drives,

• Backup the drive which you want to merge with another drive.
• Right Click on Computer -> Manage -> Storage & select "Disk Management".
• Wait for Some Time.
• Ensure that the destination drive is right side of source drive (for ex:- if you want to merge c drive with d drive then d drive must be right side of c drive).
• Right Click on the drive which you want to merge with another drive & click "Delete Volume".
• Then you will get that space as a Unallocated Disk Space.
• Right Click on the source drive & select "Extend Volume". 
• If you already have the Unallocated Disk Space then follow the above instruction.
• Now Your Drive is EXTENDED.