I have done a few of these, definitely read through the docs posted by the last poster. The other thing you can do is if you have a spare ASA you can copy the configuration onto that running the same code version that you are running currently. Then perform the upgrade to 8.6(1) and it will migrate your NAT statements and access rules automatically. I would do it offline and then compare the results Old to New, then check the document posted above for what the migration should look like.