UPDATE TABLENAME SET FIELDNAME = cast(replace(cast(FIELDNAME as nvarchar(max)),'find-this','replace-this') as ntext)
WHERE Content like '%find-this%'

http://www.sidesofmarch.com/index.php/archive/2008/02/27/how-to-use-replace-within-ntext-columns-in-sql-server/

Search and Replace String in an SQL Server nText Field

sql, search, replace

SQL