Hey @priceisrightsuperstore
The store logo is styled by the following classes - .main-logo and .main-logo img in basix > css > style.css starting at line 220 which both have a css rule max-height of 60px. So you will need to modify both of those classes to get you desired look.
The "Shop by Category" tab is 50px so the logo is already exceeding the size tab.
Also, after making any changes remember you may need to clear your browser cache as well the site cache.