Hi there driesez,
Elveon is right. Most of the software tools ask you where you want to install them. Just pick your D: partition.
Do you have data stored on your D? In case you don't have any data over there, you can go to Disk Management, delete it and extend your C: partition. Also, you can shrink your D: partition and extend your C: one.
If Disk Management doesn't allow you to do some of these, you can use some third party partition management tool.
You should always back up your data before dealing with partitions.
Cheers,
D_Know_WD
