Account and Contact relationship issue

Hi,

I created one account in IC web.in assaignment block Relationships i assaigned relationship "Has the employee responsible "

i assaigned partner id(employee).here system filled valid from and todate by default

it is filled values valid from date as 01/01/0001

valid to date as 12/31/9999

i am not able to edit these valid from date and to date in relationships

can u please explain how to change these dates

currently working on CRM 7.0

Thanks & Regards

Kishore Kumar