Hello @sully13190,
Thanks for asking and I am really sorry for the error message you are getting while updating.
In case you have already developed the website or in a advance stage of developing the website, it will be a loss of man work hours you have already invested. And there is no guarantee that the 500 error message won’t come back in future when you choose to update WordPress, plugins.
So my recommendation would be to try and find out why 500 error message is coming up and then look for some solutions. As you are trying to update WordPress and plugins and in process 500 error message is showing up, there might be a issue of memory. Please try to increase PHP Memory Limit of your server. Click here for more detailed information and how to increase the PHP memory limit.
I also suggest you to please follow some more solutions mentioned in following article:
However, if you would like to start fresh then I suggest you to delete current Theme and download latest version of X Theme from Themeforest or members area and then install the same. You can delete current version of Theme from FTP using software like Filezilla. Please navigate under /wp-content/themes/ and delete X folder.
To get started with Filezilla, please take a look at following article.
Thanks.