Hello Geert van der Aa.
Thank you so much for using our theme AcmePhotoPro. If you need to increase the logo size, you can increase the height and width defined on the theme file. Find the custom logo height and width on acmethemes/core.php file on theme folder. Change the required height and width of the logo and upload the new fresh logo from Appearance > Site Identity. Hope, you can now add the bigger logo size.
Let us know if you have any other confusions.
Regards
Acme Supports