How can I customize the map info window using Advanced Custom Fields?
Do I need to install any extra ADVANCED CUSTOM FIELDS PLUGIN plugin?
I like these examples that have in your DEMO with the image in full:
See the attached pictures.
You have to update your plugin to the latest version 5.0 we have provided multiple infowindow skins so you can customize it according to your need. Please check this our guide tutorial https://www.wpmapspro.com/docs/how-to-apply-beautiful-skins-on-an-info-window/#1