You don't have to take the head off.

Turn the engine over so it blows out the porcelain from the centre of the spark plug.

Then hammer an easy out into the remainder of the spark plug. Turn the easy out using a breaker bar. Make sure the easy out is in properly though, cos if it slips then they're really hard to get out.

Sometimes you do get a bit of crap that drops into the engine. Just turn the engine over before you put your new plugs in and it'll blow it all out. Have fun!