Whats the primary key in your database now ? You should be able to add a new column and set it to autonumber and Access will do everything for you automatically.
I realize that actually. I plan to use this but that is new record. Regarding my existing records, the primary key is to be keyed by the user, which shouldn't be. So, my plan is actually auto update a number increment by one for new record before setting it autonumber for new record.
You can still add an autonumber field to existing records and access will populate it for you.
In regards to your code, you need to tell the update which record your trying to update, just doing a select and then trying to update it won't work, basically you'll need a WHERE clause added which will determine which record is to be updated.