Getting admin access to mac with knowing the current password

Worth repeating

Change the password in single user mode

1. Hold ⌘S on startup
2. mount -uw / (fsck -fy is not needed)
3. launchctl load /System/Library/LaunchDaemons/com.apple.opendirectoryd.plist (or /System/Library/LaunchDaemons/com.apple.DirectoryServices.plist in 10.6)
4. dscl . passwd /Users/username (without a trailing slash) and enter a new password. You can ignore the error about com.apple.DirectoryServices.plist.
5. reboot

Create a new admin account

1. Hold ⌘S on startup
2. mount -uw / (fsck -fy is not needed)
3. rm /var/db/.AppleSetupDone
4. reboot
5. Go through the steps of creating a new account. You can leave all fields in the personal information step blank
6. After logging in on the new account, go to the Users & Groups preference pane
7. Select the old account, press the Reset Password... button, and enter a new password

Restart and enter Recovery mode (for 10.7 Lion and newer OS only)

1. Hold ⌘R on startup
2. Open Terminal from the Utilities menu
3. Type resetpassword and follow the instructions