If you want to quickly remove all rows from a table and begin the table from scratch TRUNCATE is the best approach. It is quicker too since it logs nothing (so beware).
TRUNCATE is only for destroying all data in a table though. What if you want to remove only the last few rows and then begin the seeding off from the last primary key?
Use CHECKIDENT to reseedYou can delete the rows you want and after you can reset the SEED of the table to what you desire using the following line:
DBCC CHECKIDENT('myTable', RESEED, 10)
Note: the 10 is a seed so you would set this to be the current maximum identity. So if you reseed with 10 the next insert will yield 11 as the primary key.