When you boot to your Linux system, select "Advanced Options", and then elect the recovery method.

From here, select root which will then bring you to shell. Now that you've selected tha, enter the following:

mount -o rw, remount /

Once there, you should then be able to update your password with the following command:

sudo passwd [your username]

This will then ask for your new Unix Password and to repeat. You can perform the same steps for root also.

You want find many tutorials online (YouTube) on how to perform this also. I note that this answer has already been posted, with a faster method, apologizes. Hope this helps!