Upgrading is fairly simple.  

You'll need one specific piece of information to complete the upgrade, the Merchant Hosted Checkout Credentials.   You'll paste these into the Live Merchant username and password fields on the plugin.
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If you are unsure how to get this, you can review the following article:

You may also be able to locate the 'active' Hosted Checkout credentials from within the Custom Meta fields on a recent order.  
If Debug is enabled within the plugin, you can view the Merchant ID and password in the first few rows of the debug data communicated to Vantiv during the order process.
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Upgrading the 1.0.x releases was a simple affair - you could delete the new software uploaded and activated - the plugin would maintain all the fields and settings from the previous plugin and apply them to the new one after it was activated.

Upgrades from 1.0.x to 2.x won't carry over the plugin details.  

You can leave the old plugin installed while you test out the new software, and migrate over as many of the fields and settings as possible.  If you have questions about the new AVS or CVV security settings, feel free to drop us a line.  

By default all of the dropdowns pre-select the suggested default options.  Once you've copied in your Hosted Checkout credentials to the Live Merchant fields, you can set the plugin to Live mode and run a test of the new plugin.  If you've left the old plugin installed, choose the correct one at checkout.  We suggest creating a Penny Test Product as shown on the article linked below.