Why do you have a hidden Partition called D:? Is it actually NOT called "D:"? Does it contain the hidden backup files used to restore your system from a Restore disk supplied by HP with your machine? If that is the case, you do NOT want to try to change it at all.
Next question to consider is where the Partitions on your HDD are physically located. If the C: "drive" is first, followed by D:, and then followed by the Unallocated Space, you cannot easily Expand the C: drive to add the Unallocated Space. Expanding only can add Unallocated Space the comes right after the Partition in question.
On the other hand, IF this hidden Partition really is the restore stuff, usually it is first on the HDD unit, and the C: drive comes after it, then the Unallocated Space after that. In that case, Expanding is possible.
HOWEVER, there is still a problem. Although Windows can Expand a Partition to add on Unallocated Space which is immediately adjacent, it will NOT do this for any Partition that contains the OS and Virtual Memory file. This is to be sure you don't lose your whole system if a glitch happens. Now, some other third-party software that you can buy, like Partition Magic, can and will do that job. But Windows does not have the tool for it.