Which is more costly, to create a new table or alter current table in postgresql?

I have Table(table_1) has one column "column_1" as primary key and I need to : 1. add 3 other columns (column_2: serial, column_3 : integer , column_4 :Date) 2. Drop current Primary Key Constraint My Question is : Which is better (DB performance, Best Practices ) create new table or Alter Current table ?