SQL update next row in select
Do you actually need to persist the prev and next columns in the data? Why not use Window functions on retrieval of data to get what you need from your base table? I've made a bit of a guess on what your schema looks like in it's most basic form but this should help you. If not post CREATE statements for all tables involved and I'll edit the answer.

SELECT  MonthDate
        , CarId
        , KM
        , LAG(KM) OVER (PARTITION BY CarId ORDER BY MonthDate) Prev
        , LEAD(KM) OVER (PARTITION BY CarId ORDER BY MonthDate) [next]


FROM    PrevNextFullList


If you do need to persist the columns then use this statement to create a VIEW

UPDATE You would need to upgrade to SQL 2012 to do this though.