to reset your password:

• Power down and pull the SD card out from your Pi and put it into your computer.
• Open the file 'cmdline.txt' and add 'init=/bin/sh' to the end. This will cause the machine to boot to single user mode.
• Put the SD card back in the Pi and boot.
• When the prompt comes up, type 'su' to log in as root (no password needed).
• Type "passwd pi" and then follow the prompts to enter a new password.
• Shut the machine down, then pull the card again and put the cmdline.txt file back the way it was by removing the 'init=/bin/sh' bit.

more information: http://mapledyne.com/ideas/2015/8/4/reset-lost-admin-password-for-raspberry-pi

Hope this helps!

to reset your password:

• Power down and pull the SD card out from your Pi and put it into your computer.
• Open the file 'cmdline.txt' and add 'init=/bin/sh' to the end. This will cause the machine to boot to single user mode.
• Put the SD card back in the Pi and boot.
• When the prompt comes up, type 'su' to log in as root (no password needed).
• Type "passwd pi" and then follow the prompts to enter a new password.
• Shut the machine down, then pull the card again and put the cmdline.txt file back the way it was by removing the 'init=/bin/sh' bit.

more information: https://web.archive.org/web/20160228052651/http://mapledyne.com/ideas/2015/8/4/reset-lost-admin-password-for-raspberry-pi

Hope this helps!