For version 1.9.3+ :
Go to WP Admin -> WPLMS -> Miscellaneous -> Custom CSS for Login screen :
Add this code :
body.login h1 a{
width:160px;
height:400px;
}
Adjust the width and height according to your requirements.
You can use this section for various other styling options as well :

For version < 1.9.2
1. Go to WP Admin -> Plugins -> WPLMS customizer -> customizer-_class.php
2. Add this code in __construct function
PHP Code:
add_action( 'login_enqueue_scripts',array($this, 'vibe_login_logo' ));
3. Add this code in the class:
PHP Code:
function vibe_login_logo() {
?>
<style type="text/css">`
.login h1 a{
width:160px;
height:400px;
}
</style>
<?php
}