You c an use this trick to create a new admin account - then you can change the other passwords.
Make sure the you do not space in between the db/.Apple and use capital letters where they are in the code and it will work
# Hold apple + s down after you hear the chime.
# When you get text prompt enter in these terminal commands to create a brand new admin account (hitting return after each line):
* mount -uw /
* rm /var/db/.AppleSetupDone
* shutdown -h now
# After rebooting you should have a brand new admin account. When you login as the new admin you can simply delete the old one and you're good to go again!