I ALWAYS remove them by punching a hole in them with a hammer and sharp punch. If you can't get a hammer close in, then use a "ladyfoot" (tool store or truck will know what they are), and a hammer.
Then pry out. You can also use a dime/nickle size flat punch, and knock in one side, which will cause it to flip the other side out.
They can be a real bitch.
We had a '79 landcruiser in a while back, and those plugs just did not want to come out. Took forever and many different tools.
Be sure and sand the block holes to get all the rust and corrosion off before installing the new ones.
You'll also need a freeze plug installation set to get them in correctly.