How to make the Logo smaller?

You should be able to simply decrease the image size in Photoshop or an online image editor and reupload it into Appearance > Customize > Site Identity > Logo. Otherwise, you should be able to modify the below CSS pixels:

#masthead .site-branding > a > img {
    max-width: 510px;
}

This would be added to Customize > Additional CSS.

try this

.site-branding img {
width: 50%;
}

Hi guys, thanks so much!
The width: 50% worked like a charm.
WOOHOO!

All the best,
Brian