Talking directly to the board, Changing password,

If you don't have ssh installed, install it. (google is your friend) Then ssh debian@192.168.7.2 The board will tell you what the password is, on my it was "temppwd".

To change your password use the command passwd it will ask you what your current password is, then ask for the replacement. Then it will say it was too simple and you have to do it again. Normal stuff.

If you want to insist on using your simple password, try this.

sudo -s
(become superuser/root)
enter your password
passwd debian
 (put your simple password in)
exit
(exit from superuser/root) 

When you are running as root, passwd is more compliant and will accept simple password