Depending on how you would want to deal with possible NULL values, concat_ws() is probably your safest and simplest way to go:

UPDATE tbl
SET filed1 = replace(field1, concat_ws(' ', field2, field3, field4), '')

Depending on how you would want to deal with possible NULL values, concat_ws() is probably your safest and simplest way to go:

UPDATE tbl
SET filed1 = replace(field1, concat_ws(' ', field2, field3, field4), '')
WHERE filed1 IS DISTINCT FROM replace(field1, concat_ws(' ', field2, field3, field4), '')

concat_ws() ignores NULL values. With plain concatenation (||), one NULL field would make the whole pattern NULL. It was introduced with Postgres 9.1.

The added WHERE clause prevents empty updates. This enhances performance a lot if many rows wouldn't change anyway.