[sql-server] How to remove not null constraint in sql server using query

I am trying to remove not null constraint in sql server 2008 without losing data.

Remove column constraint: not null to null

ALTER TABLE test ALTER COLUMN column_01 DROP NOT NULL;

Reference: https://www.tutorialspoint.com/How-can-we-remove-NOT-NULL-constraint-from-a-column-of-an-existing-MySQL-table

ALTER TABLE tableName MODIFY columnName columnType NULL;

Remove constraint not null to null

ALTER TABLE 'test' CHANGE COLUMN 'testColumn' 'testColumn' datatype NULL;