alter column to not null that has null values

I have to change numeric columns in 2005 table to not null and default value 0.

What I usually do is an update on the columns setting value to 0 where is null. I know you can use 'with values' when adding a column with default 0 and not null to an existing table.

Can something like this be done for altering a column or do I need to do the update?

Thanks

You need to use UPDATE first and then ALTER. ALTER TABLE table ALTER COLUMN only supports changing the type definition, collation and nullability.