Procedure: Reset FreeBSD root user password

Step # 1: Start FreeBSD server/workstation

Step # 2: Press Enter key at boot loader

At Welcome to FreeBSD! boot menu press spacebar key to pause default booting

Type number 4 key (type 4 number) to boot into single user mode

(click to enlarge)

Next you will see following prompt from system:
When prompted Enter full pathname of shell or RETURN for /bin/sh:

Press Enter key to boot into single user mode. Next, you will be immediately dropped into a single user mode without a root password.

You need to remount / (root) file system in read and write mode with mount command, type following two commands:
# mount -u /
# mount -a

Setup a new password with passwd command:
# passwd

Next type exit command to boot FreeBSD into multi-user mode environment:
# exit
OR You can just reboot the system:
# sync;sync
# reboot

For more information read man pages of passwd and mount command.