Please note, you can request the new update of Booking Calendar on this page.
A) Probably at your computer was set properties for the archive files to show as folder and that's why you see it as a folder.
Please check in your explorer to show the extension of the files. Then try to download it again and make upload to your website.
B) Or you can upload entire folder (not zip file) to your serve by FTP (skip 2 first points) :
1) Please download the archive of the Booking Calendar to your desktop.
2) Extract it from archive. You have to get the "booking" folder.
3) Please upload this folder, using the FTP manager to your server, to the folder ../wp-content/plugins/
If you do not have access to your server through FTP, then please contact support of your hosting company about this details.
4) Now open admin panel of your WordPress site at the Plugins menu, you have to see there Booking Calendar plugin. (If you was having previous free version, there, please deactivate it).
Please click at the "Activate" link of your new paid version.
5) Please wait until message will show that the plugin is activated successfully.
Now you have to be able to use Booking Calendar plugin.