Small Engines (Lawn Mowers, etc.): 12 hp briggs seized up, murry lawn mower, hp briggs

Question
I have a Murry lawn mower with 12hp briuggs engine.
Mower wasn't ideal for mowing my 3 acres of land so I bought a tractor and let my kid use the Murry for riding around property. Yes I disabled the mower part.
Well Kid let mower run out of oil. I never have repaird a seized engine before but was wanting to try.  Need pointes on starting first.
Thanks  

Answer
this happens more often than you would think, first how much money do you want to put in this tractor,and if you dont want to spend more than 50$ depending on how bad it is stuck you may be able to spray penetrating fluid in the cylinder through the spark plug hole and turn it backward one whole turn and then use the starter to turn it over without the spark plug in it being careful because the penetrating fluid will come back out the hole after putting fresh oil in of course this sometimes works to get some extra life out of it