If you just made changes to your FE no issues.  You just have to link the development copy back to the "live" working BE and distribute the new FE to all your users.  See the Access Updater for making that part easier.

If you just added tables to the Dev BE those can be copied into the live BE. You will need to delete any 'test' data so you don't have inaccurate info in your live db.

If you made structure changes to the existing BE tables different story.  You will have to either make those same changes to the live BE or put the whole Dev BE in the place of the live BE and import or update the tables with the live data.

I should add that the changes to the live db will need to be done when you can have exclusive access to both the FE and BE.  No one else can be in the DB while you are changing things in the live BE.
So... either at night or on a weekend.
I'm glad you used a copy to develop in!  Before making any changes to the live FE & BE be sure to have good backups just in case the upgrade doesn't go according to plans.

Speaking from experience -
   0.  BACKUP!
   1. Write out a game plan of what you need to do.
   2. Allow plenty of time. Don't do it if you are rushed. That is when mistakes are made. If you think it
       will take you an hour, allow 3.  Good old Murphey shows up regularly when you are making changes.
   3. In the future keep a note pad document open at all times and record any changes you make in the
       BE tables to facilitate easier upgrade process.

Thank you. All great advice.  Will try it.