Reducing the "mininum" username length allowed

as you should know, new users should have a username from3 to 40 characters, the question is, what should i change if i want usernames with 2 characters or even 1 character?

i use miniBB integrated with an existing user's data, and there are some usernames with 2 characteres, and i they try to change their user's preferences at miniBB, they just can not do it.. it appears and "username error data" saying the characters stuff..

any idea?

bb_func_checkusr.php -
$userRegExp="#^[".$userRegName."]{3,40}\$#";

thanks.