From google
To remove a rounded spark plug from a Hemi, first apply a penetrant spray like PB Blaster to the plug and allow it to soak. Then, try hammering a smaller, specialty spark plug socket or a bolt/stud extractor over the rounded plug to bite into the remaining metal. Once seated, carefully twist to remove the plug. Be sure to clear debris from the cylinder after removing the plug.
Preparation
1. Soak the plug:
Spray a good penetrating oil (like PB Blaster) around the base of the spark plug and let it soak to loosen any corrosion or carbon.
2. Allow engine to cool:
Make sure the engine is completely cold before attempting removal, as aluminum heads expand when hot.
3. Check for debris:
Use compressed air or a long pick to clear away any loose dirt or debris from around the spark plug.
Extraction Methods
Specialized Sockets:
Hammer a smaller-than-standard, 12-point socket or a spark plug extractor socket over the rounded hex. The socket will expand slightly from the heat and can be hammered on.
Heating the socket:
Heat a slightly oversized socket with a torch until it's hot, then tap it onto the rounded spark plug. As the socket cools, it will contract and grip the plug, allowing you to remove it.
Using a "hammer-on" socket:
A socket designed to be hammered onto a rounded nut or bolt can bite into the remaining metal.
Alternating tightening/loosening:
If you feel any movement, tighten the plug slightly and then loosen it back. Repeat this process in small increments to break the spark plug free.
I hope this helps
