Fdisk, supplied with DOS/Windows will delete the unwanted partions. It won't resize a partition without destroying your data.
As long as you are prepared to wipe the data on the disk, the basic steps are to:
You will need a bootable floppy with Fdisk & Format on it.
With 'Fdisk'
1. At the DOS prompt type "Fdisk" & follow the instructions to delete all partions
2. Create the desired partition.
Now with 'Format'
3. At a DOS prompt type "Format C:" & follow the instructions...
If you want to try to resize the partition without losing data then you will need a 3rd party tool eg 'Partition Magic' or 'Ranish Partition Manager', 'Diskdrake' from Linux etc.
Partition Magic (PM) will cost you but has a reasonably friendly graphical interface.
Ranish Partition Manager is free but doesn't have the graphical interface. In my experience it is more capable than PM but more difficult to use.
It was able to get me out of trouble that was caused by a PM caused problem. PM wasn't able to fix it itself.
Alternatively, you could use one of the Linux based partition tools. These are also free & can set the partition structure to a range of types, including DOS.
Diskdrake (comes with Linux Mandrake) is graphical, easy to use & I think more capable than PM.
I can email you a copy of Ranish if you like. It's only 30 or 50 Kb in size.