How to delete one of the 3 operating systems?

I have 3 operating systems on a single hard disk partitions and would like to know how to delete one of them

In a same partition 3 systems?
That's impossible, at least in my opinion.
What we'll certainly are 3 partitions with 1 in each system.
To remove a can use Partition Magic that will unite two partitions in a resizing space.

I think the same thing that my colleague, or better if you do not want to use Partition Magic able to use fdisk DOS.

here is the instruction as to how you can get rid of second operating system:

http://support.microsoft.com/default...;EN-US;q289022

Hope this helps you!