http error 500 / Internal Server Error
Internal Server Error 500 is usually related to server settings as the name of the error suggests.
There could be several causes of this problem. First you should do is contact your hosting provider and ask them about this, and also ask them to check your error log, to see what does it say there?
Also, read this article http://www.wpbeginner.com/wp-tutorials/how-to-fix-the-internal-server-error-in-wordpress/
And try the solutions from it, increasing your memory_limit parameter first, it could be low and that could be the cause of this.
And also, it is good if you can increase these values or ask your hosting service to do that for you.
max_execution_time = 300
memory_limit = 128M
upload_max_filesize = 128M
post_max_size = 256M