I had to create a work item template.In order to do it quickly.I created all the fields by opening the template in notepad and copy pasting them with differnent name but same datatype.

Then I import the template. Now I am trying to change the datatype form Open Wit from Server option , it is throwing me errors that datatype do not match . So I deleted those fields and reimported the templated.It is still throwing me the same error. I notice when I open work item field explorer then I can see the fields there. Even I have deleted them form workitem template. 

So my question how can I delete Fields and work items.