Prior to OS X Lion, the OS X installation DVD included a password reset utility. With Lion there is no install DVD, and no easily recognizable way to reset a password for a user account. Don’t worry, if you ever forget your password for a Lion user account, there is still a way to reset it; in fact it’s much easier than booting from a slow DVD.
Restart your Mac while holding Command + R. This will boot you into the Recovery HD Utility. Launch the Terminal from the Utility menu at the top and type resetpassword and hit enter. The Reset Password dialog box will appear where you can choose which user account password you wish to reset, and allow you to enter a new password and hint.