Merging local disk drives

After creating a back-up for my dell XPS8500, somehow the C: drive is divided into partitions. I reset  the PC to the factory default but the C: drive is not the same as when I first got it (still divided). Now it has C: drive and D: drive ( same primary disk ) . How can I merge D: into C:  ? C: and D: is not next to each other .

Thanks for your inputs.