Sorry to dig this up from the grave, but I needed to do the same thing, this is how I did it:
FTP to the /wp-content/plugins/wp-members/ folder or use the editor built into wordpress and edit the following files in the following way:
In wp-members-dialogs.php find and comment out the following code (around line 696)
if( $toggle == 'edit' ) {
$form = $form . '<label for="username" class="text">' . __( 'Username', 'wp-members' ) . '</label>
<div class="div_text"><p class="noinput">' .
$userdata->user_login .
'</p></div>';
} else {
$form = $form . '<label for="username" class="text">' . __( 'Choose a Username', 'wp-members' ) . '<font class="req">*</font></label>
<div class="div_text">
<input name="log" type="text" value="' . stripslashes( $username ) . '" class="username" id="username" />
</div>';
}
And in wp-members-register.php replace:
$username = $_POST['log'];
with
$username = $_POST['user_email'];
and comment out the following
if( !validate_username( $username ) ) { $wpmem_themsg = __( 'The username cannot include non-alphanumeric characters.', 'wp-members' ); return $wpmem_themsg; exit(); }
Upload to server/save changes.
