database timing out when we delete records

We need a solution to a problem deleting records from a large SQL Server database. It is a database with logs of hits on 50 or 60 websites for each day over a period of 9 months. We need to delete old records because the database is getting too big and too slow to run queries. It is very slow deleting the records from the database because for example if you write, "delete from tracking where accessdate <='2007/07/31'" it will timeout and you have to delete one day at a time. We need to see why this is happening and be able to delete a whole month without it timing out.