It would probably help if you mention the engine involved.

In general, 'freeze' plugs, or Welch plugs are extremely simple to
remove, if you can get to them.  A sharp punch or a screwdriver
can be used to puncture them, and you just leverage them out.

Tapping in the new set is easy if you have a socket wrench or
tool of proper size to put inside th concave part of the plug, and
gently hammer them in.

If you can get them out, but dont have room to tap in the new ones,
you can either lift the engine, disconnect motor mounts, etc, OR you
can install expandable rubber plugs.