To be honest before i grabbed the hack saw i would always set up a straight 6 pipe wrench inside the toilet tank and position it at the base of the fill valve with the handle up against the toilet tank.
Toilet lock nut clockwise.
I then would proceed counter clockwise with a second offset 6 pipe wrench and try to loosen the nut.
Remove the nut washer and lock nut.
Remove the fill valve.
Tightly secure the lock nut washer and nut.
Empty the bucket and place it underneath the water supply line.
Position the new valve in place of the faulty one.
While turning these stabilize the bolt from above with a screwdriver.
Then finish loosening the nut with your fingers.
Some nuts have wings that you can grasp with your fingers.
The end of the water supply line will come away from the connection.
Locate the coupling nut on the underside of the toilet tank.
Raise the pipeline from the overflow tube.
These are used in a toilet chiefly to secure the fill valve in the toilet tank.
Prepare the toilet turn the water supply shutoff valve clockwise to turn.
The lock nut threads onto the fill valve inlet just above where the water supply hose or tube coupling attaches.
Step 3 replace the valve.
If the nuts don t have wings lock a pair of locking pliers around each one in turn.
Gently pull the nut down.
Lock nuts are used to hold fixtures securely in place from below.
When you unscrew the screw the pliers will hit against the toilet bowl and prevent the nut from turning and it will loosen.
Use your pliers to loosen the nut under the tank.