Use sp_rename
EXEC sp_RENAME 'TableName.OldColumnName' , 'NewColumnName', 'COLUMN'
See: SQL SERVER – How to Rename a Column Name or Table Name
Documentation: sp_rename (Transact-SQL)
For your case it would be:
EXEC sp_RENAME 'table_name.old_name', 'new_name', 'COLUMN'
Remember to use single quotes to enclose your values.