As Colif said, you need to go to Disk Management.
Do you have data stored on the D: partition? In case you don't you can just delete the partition, you will get some unallocated space, and then right click on your C: partition and extend it.
Alternatively, you can use some partition management tool: http://www.tomshardware.co.uk/forum/277170-32-best-partitioning-software
One other thing you can consider is to free up some space on your C: partition. Here's an extensive tutorial on how to do that: http://www.howtogeek.com/125923/7-ways-to-free-up-hard-disk-space-on-windows/
As Colif said, you need to go to Disk Management.
Do you have data stored on the D: partition? In case you don't you can just delete the partition, you will get some unallocated space, and then right click on your C: partition and extend it.
Alternatively, you can use some partition management tool: http://www.tomshardware.co.uk/forum/277170-32-best-partitioning-software
One other thing you can consider is to free up some space on your C: partition. Here's an extensive tutorial on how to do that: http://www.howtogeek.com/125923/7-ways-to-free-up-hard-disk-space-on-windows/