I have bought a MacBook Pro, and I'm having problems with those passwords.
How can I disable them completely?
There are two methods according to OS X Daily.
I don't have a 10.7 machine to try but I would assume they work fine.
Plain password reset
Reboot your Mac and hold the
Here, type in the following and press
This is pretty straightforward.
Making the Mac forget it's been set up
Do the same as above, where you boot into the Recovery disk. Select Utilities → Terminal again. Then, enter the following:
After that, enter
Your Mac will now think it's been freshly unpacked. You can create a new administrator account through the steps here. For example, call it "temp". Once you're done with the setup, you can log into your new account.
Then, open System Preferences → Users and Groups. Click the lock to authenticate. From the user list on the left side, click the account you didn't know the password of. Here, click "Reset Password".
Once you're done, you can log out from your "temp" user, and log into the other user again.
You can even remove the "temp" user by going to Users and Groups preferences from the original user account and deleting it from there.