Unless someone has Billy Bobbed the sight, removal is to push out the pin.
Note that the pin is staked in place.
What's required is to get the barrel and sight in a no-bounce, no-move setup by bracing with hardwood blocks.
If anything moves when it's struck, the pin will not budge, and it might be distorted and locked even tighter.
Start out with a "starter punch". This is just a standard punch that's been cut off to about 3/4" working length.
This prevents the punch from flexing or bending, dissipating the force.
Once you get the pin moving, then use a standard length punch.
With the pin out, the entire sight and band has to be pushed STRAIGHT forward and off the barrel.
The sight has a "key" under it that locks into a key way in the barrel. DO NOT try to rotate or turn the sight.
Note that many Carbine sights are on TIGHT, and the Ordnance people used a special front sight removal and installation tool set.
The removal tool worked something like a gear puller.
Use a hardwood block or brass or nylon drift to tap the band forward. Make sure to tap all the way around the band not just on the sight area.
Trying to drive the band off by tapping in one area can distort the band, locking it even tighter.