How to replace a string in a SQL Server Table Column

UPDATE [table]
SET [column] = REPLACE([column], '/foo/', '/bar/')

I tried the above but it did not yield the correct result. The following one does:

update table
set path = replace(path, 'oldstring', 'newstring') where path = 'oldstring'

It's this easy:

update my_table
set path = replace(path, 'oldstring', 'newstring')

UPDATE CustomReports_Ta
SET vchFilter = REPLACE(CAST(vchFilter AS nvarchar(max)), '\\Ingl-report\Templates', 'C:\Customer_Templates')
where CAST(vchFilter AS nvarchar(max)) LIKE '%\\Ingl-report\Templates%'

Without the CAST function I got an error

Argument data type ntext is invalid for argument 1 of replace function.