Hello Luis ,
In such case ,you need to manully set/change the Contract ->End Date.
Changing the End Date again depends on the status of Contract .If the Contract is with status as
'In Preparation' / 'In Process' ,then you can change the 'End Date' in the General tab of Contract.
***Note : You have to also keep note of ,End Date in General tab (Header) cannot be set/kept
less than(prior to) End Date within Contract->Item level(In case dates are different in Item and Header).
Hope this answer your query ?
Regards,
Ankush.