Cannot remove CalPress

A new client has asked me to manage their website. It was old and required a lot of fixes and updates.

One plugin, CalPress Pro, was throwing fatal errors. I explored how it had been used, and could not find a lot of data past 2013, so I tried to disable it and delete it – it won’t delete – it just throws more errors.

They had the pro version (at least in 2013), but I can’t figure out any way to extract that program!

I renamed the folder and the tables, but that didn’t remove the program. I searched for references to calp and calpress in the database and examined what I found, but I was a little concerned about trying to extract them from wp_options and other table rows without messing something eles up.

I suspect that upgrading from WP 4.5.19 to the current 5.4.2, and by necessity, putting it on my server which runs PHP 7.3 might have contributed to the problem – it was running on PHP 5.2.17.

Is it safe to delete the tables and the folder? Will that be enough to clean it out of the upgraded website?

Thank you,
Ernie