Internal server error

My site suddenly crashed due to a plugin misbehavior. Then suddenly upon developing another workbook update to my product it also replied me a “500 internal server error” while trying to activate my new workbook.
what does it mean and how to fix it?
internal server error

Please check your PHP error log. Did you change your PHP version recently?

Yes i recently change version as per suggested by WordPress. What would i do?

Tweak your PHP.ini so that obsolete and deprecated features of PHP are not considered as fatal errors. It’s the error_reporting entry. If you don’t know how to do it, ask your web hosting support team.