Delete all Records in the Table and then Compact the database.
OTOH, the only purpose of AutoNumber Field is to provide uniqueness to each
Record in the Table and the actual value allocated to each Record should not
matter.
AutoNumber values will develop gaps in the sequence, become negative or even
random (in replication). In my applications, users don't even see the
values of AutoNumber Fields for the above reason.
Beware that attaching some meaning to AutoNumber values may create problems
in the database later. If you need to attach some significance to the
values, AutoNumber may not be the correct Field type to use.