I believe that if you remove all the data from your table, and do a compact and repair, that this will reset the auto number.
However having said that, the only thing you can rely on the auto number to do, is to to produce a unique key for each record. It may not always provide a consecutive number and it may even provide a negative number under certain situations.
If what you are wanting a consecutive incrementing numbers search this forum on the subject of using Dmax()+1 to provide this result.