From Resetting SQL Server Identity Columns:
Retrieving the identity for the table Employees:
DBCC checkident ('Employees')
Repairing the identity seed (if for some reason the database is inserting duplicate identities):
DBCC checkident ('Employees', reseed)
Changing the identity seed for the table Employees to 1000:
DBCC checkident ('Employees', reseed, 1000)
The next row inserted will begin at 1001.