How to repartition the hard drive on my Asus B53F laptop?

I’m assuming D is just a data partition and doesn’t contain the page file, boot files or a second operating system. If so, merge the partitions by removing D and extending C, as follows:

1. Back up to an external device any important data on D and, optionally, move the same important data from D to C.

2. Right-click Computer > Manage > Storage > Disk Management, then right-click the graphic of the D partition and select Delete. The partition returns to Unallocated for a Primary Partition or Free Space if it‘s a Logical Drive within an Extended Partition. Delete the partition if it is an Extended partition.

3. Now right-click the graphic of the C partition and select Extend.