How do I update different columns and rows across a table? I want to do something similiar to replace a string in SQL server

I want to do this but the value exists in multiple columns of the same type. The values are foreign keys varchars to an employee table. Each column represents a task, so the same employee may be assigned to several tasks in a record and those tasks will vary between records. How can I do this effectively? Basically something of a replace all accross varying columns throughout a table.

Thanks for any help or advice.

Cheers, ~ck in San Diego