Carbine receivers, even most non-GI are pretty hard, and you can chip or even break the receiver or dovetail.
Ordnance used a special sight puller device to remove and install sights.
Use a large brass or nylon drift.
Get the receiver in a well braced, no-bounce setup using wood blocks.
If anything moves or bounces when struck, the force is dissipated, and the sight won't move.
This can cause the sight to distort, locking it tighter in place and causing damage to the sight or receiver.
Place the drift on the BOTTOM of the sight base, close to the receiver dovetail.
This will prevent bending the sight, and will better move it than striking near the top.
Tap the sight out, from left to right, then use solvent to clean the dovetail, and the new sights dovetail.
Apply lube and test fit the sight.
It should be fairly tight, but not so tight something breaks from being hammered in with too much force.
Carefully drive it in placing the punch low as when removing, and center the sight in the dovetail.
If the sight is TOO loose or tends to shift, remove the lube and use Loctite Blue, (temporary) to secure the sight. Allow a full 24 hours to cure, then apply lube to prevent rust.