I have a manual for an older 8 HP Briggs motor and the specs are probably about the same. It is in pdf format so I can email it to you if you want it.

start it up and warm the engine. remove the drain plug at the bottom of the block (usually has two one at the front and one at the back). Remove the easiest one to get to usually the one sticking out front. raise the back by the handles to let all the old oil drain out. Put the plug back in. remember the plug will have pipe threads (taped) Snug it but don't over tighten it. Level out the engine and pour the fresh oil down the dip stick tube of course with the dip stick removed. Drop the dipstick in and get it in the XXXXXXX area, start it up let it run for a couple of minutes then shut it off. after 5 mins check the level of oil and top it off to the top of the XXXXXX area on the dip stick.

one step that rcmoser left i that i hope you know but will mention anyway is that after the tiller warms up, shut it OFF before removing the drain plug!

i mention this because i gave my brother similar instructions once and he tried to remove the plug with the engine running. got a nice coating of oil everywhere.