Just format the D: drive ...
As for your first query, there are many methods to do that:
FDISK method:
You can delete F: and H: , and from the unallocated space, create a new partition.
Diskmanagement tool:
You can use the DiskManagement tool (Control Panel->Adminstrative tools -> Computer management), delete both your partitions, and from the unallocated space, you can create a new one.
IF you want to non-destructively join both the drives (ie, if they contain data that you cannot move elsewhere)
Get Partition Magic (or even a boot disk containg PM will do) , select both the partitions, and choose the option merge.
