500 Internal Server error when upload items

I get the following error when I try to upload .jpg files:

Internal Server Error

The server encountered an internal error or misconfiguration and was unable to complete your request.

Please contact the server administrator, webmaster@allenstownlibrary.org and inform them of the time the error occurred, and anything you might have done that may have caused the error.

More information about this error may be available in the server error log.

Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.

I believe this is due to the file size, as the .jpg files smaller than 6571kb loaded fine. Reading other forum posts, it appears it's a server issue. Can you explain what I need to change on the server or something, to upload larger files? Thanks.

Our server is hosted by Namecheap
I am using Omeka 2.0.2

Have you tried following the instructions on retrieving error messages?

You could also check with your host to see if they have any error logs or information that could be helpful.