UPDATETEXT function is useful.
This feature will be removed in a future version of Microsoft SQL Server. Avoid using this feature in new development work, and plan to modify applications that currently use this feature. Use the large-value data types and the .WRITE clause of the UPDATE statement instead.
Here is an example taken from Books Online. It is little tricky to manipulate text columns in SQL Server.
DECLARE @ptrval binary(16)
SELECT @ptrval = TEXTPTR(pr_info)
FROM pub_info pr, publishers p
WHERE p.pub_id = pr.pub_id
AND p.pub_name = 'New Moon Books'
UPDATETEXT pub_info.pr_info @ptrval 88 1 'b';