Try soaking them in hot soapy water first if they're tricky to remove. Use soapy water to make sure that the jar is clean before sterilising. Take care to rinse off all the washing up liquid. Place in the microwave (while still wet) and turn on 'high' (usually around 1,000 watts) for 30-45 seconds.
Now that we've gotten the safety stuff out of the way, the quickest way to sterilise jars in the microwave is just to wash your jar in hot soapy water, and rinse as before. Then place your wet jar in the microwave on full power for about 45 seconds (or until bone dry).