How do I destroy an object created from a simple class?

Three ways:
1) Delete all references to it by overwriting each and every variable which refers to the instance you want to get rid off and wait. At some point the Garbage Collector will get called in, and will Dispose of it for you automatically (or your app will end first)

myVariable = null;

2) Manually call Dispose on the instance you want to get rid of:

if (myVariable != null)
   {
   myVariable.Dispose();
   myVariable = null;
   }

3) Create the instance at the start of a using block, and the system will automatically call Dispose for you when the variable goes out of scope:

using (MyType myVariable = new MyType())
   {
   .. use myVariable here ...
   }