Change Logo Image Size (Silk-Lite theme)

I am using silk-lite theme. This contains a site-logo with the same image size.

When I examine the code the following is attributed to the site-logo:

“class=”site-logo-link” itemprop=”url” rel=”home” href=”http://mywebsite.com/”>

I have tried placing various options into funtions.php; the latest being:
add_image_size( ‘silk-site-logo’, 90, 56, true );
add_theme_support(‘site-logo’, array(
‘size’ => ‘silk-site-logo’))

But this is not working.

Can you please direct me as to how to change the image size of the logo for this theme please?