Hello Lars,
Thank you so much for your theme purchase and thanks for your question regarding our theme. We really feel happy to help our clients. As per your question, free theme can’t automatically update to pro version, you have to add it manually.
Go to Appearance > Themes > Add New > Upload(Upload the Zip file of the theme ‘acmeblogpro.zip’) and activate it.
Of you can upload if through FTP(wp-contents/themes/upload the folder ‘acmeblogpro’ not zip file).
If you have any question, don’t hesitate to ask. Our dedicated support forum will answer you.
Kind Regards,
Acme Supports