Hi Lenny
Here are the steps you need to take.
Build your test environment.
Be sure to install Dynamics GP 2010 v11.00.2248
Have your users run pre-upgrade reports in the production environment
Backup your databases
Move the DYNAMICS and company databases to the test environment.
Also move your reports.dic and forms.dic files if they exist. Look out for 3rd party dictionaries as well
Restore your databases into the test server.
Launch Dynamics GP Utilities and update your GP 2010 databases to the latest version
Update your reports and forms dictionaries to the latest version
Backup your databases and updated reports and forms dictionaries
Install GP G2015 R2 v14.00725
Launch Dynamics Utilities and upgrade the databases to this version
Upgrade your Reports and forms dictionaries
Backup your databases and reports and forms dictionaries
Install GP2016 R2
Launch Dynamics GP Utilities and upgrade your databases
Upgrade your Reports and forms dictionaries
At this point you can have your users run the post upgrade repots and validate the upgraded data.
I haven't mentioned that you must upgrade any 3rd party products you at each version level, so don't forget to do that.
Also, you may be changing the SQL Server version you are using so be sure to change the SQL version level as well.