Website backend running slow, difficult to make changes, might need cron job adjustment

I have a real estate website that needs to be updated frequently. The wordpress editor is normally not this slow or difficult to make changes. Tech support told me this was the issue: "It looks like the issue from the account is coming from your wordpress installation and some of the plugins on it running several cron jobs. These cron jobs look to try and take all the available resources to push the job through as soon as possible. In these cases what we recommend installing the WP Crontrol plugin as within it you can change the cron schedules. Usually the cron jobs try to run every 5 minutes to every hour where they should really be set to once a day or once a week." I have no idea how to go about this. They also mentioned something about me not having enough media space left, which could be contributing to the slowness and errors. Also received an error trying to update to wordpress 5.0.3. : "Internal Server Error The server encountered an internal error or misconfiguration and was unable to complete your request. Please contact the server administrator at webmaster@[login to view URL] to inform them of the time this error occurred, and the actions you performed just before this error. More information about this error may be available in the server error log. Additionally, a 500 Internal Server Error error was encountered while trying to use an ErrorDocument to handle the request." Need help getting this all resolved so the website runs smoothly and as normal.