Просто используйте функцию замены в T-SQL
declare @myOriginalString varchar(50)
set @myOriginalString = 'ABC DEF'
declare @myfindstring varchar(50)
set @myfindstring = 'DEF'
declare @myReplaceString varchar(50)
set @myReplaceString = 'XYZ'
select replace(@myOriginalString,@myFindString, @myReplaceString)