Increment The Value

If there is one field such as Seq No in a table and if we entered some data ..
and if we update one record of Seq No then the below records of Seq No should be incremented in that table

for example there are 10 seq no's and if i had updated the seq no 4 to 5 then the
5 shuld b inc 6 and 6 to 7 etc............

at preasent i wrote only
update in sp of that particular record:
like this

set ANSI_NULLS ON
set QUOTED_IDENTIFIER ON
go


ALTER PROCEDURE [dbo].[UpdateSelected]
(

@Description NVARCHAR(30),
@SequenceNo int
)
AS

UPDATE Sequence SET
Description = @Description,
SequenceNo = @SequenceNo

WHERE
SectionID = @SectionID
but now i need additional functionaly like inc the remaining sq no above that given no...

Regards,
Anushka