List import using Powershell sharepoint 2010

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PowerShell

SharePoint2010

i have one list for example

list 1 emp, at location 1

name-----empid------salary

emp1------1---------123
emp2------ 2------563

now when i export this list to location 2

it will be imported as it is

but now i make changes in list at location 1, i will change employee 1 name i.e. item number 1

name------empid------salary

emp111 ------1------ 123
emp2------ 2 ------ 563


and when i import to location 2 using import command in power shell

it should be like above one but it is not list will be like


name------empid------salary

emp1 ------1------ 123
emp2------ 2 ------ 563
emp111 ------1------ 123


items are getting appended i don't want that any one having idea