Seafoam, change the oil and plugs, then Auto-RX. Don't want the ARX wasting itself attacking the Seafoam remnants in the oil. And if it's the first time you've Seafoamed, your plugs will likely be all junked up from the carbon knocked loose from the Seafoam.
Also, go about 100-200 miles after Seafoaming before changing the old oil to ensure all the Seafoam traces have been washed into the oil.