To delete the first 1000 rows:

DELETE TOP(1000) FROM TableName

To delete the last 1000 rows:

DELETE FROM TableName WHERE PrimaryKeyColumn IN (
  SELECT TOP(1000) PrimaryKeyColumn FROM TableName ORDER BY PrimaryKeyColumn DESC
)

Delete FROM Customers where CustomerID = (select max(CustomerID) from Customers) or CustomerID = (select min(CustomerID) from Customers);