We can create custom Error Pages using .htaccess file. Still you've a chance to update error pages, updating apache configuration.

Now first create .htaccess file. Enter following code inside:

<Files .htaccess> 
order allow,deny
deny from all
</Files>
ErrorDocument 404 /errordocs/error404.htm

This pretty code, tells apache to redirect client to error.html page.

ErrorDocument 404 /error.html

404 tells server that, if an Page Not Found error occurred, send client to that page (error.html).

Orther error code are

400 - Bad request
401 - Authorization Required
403 - Forbidden directory
404 - Page not found
500 - Internal Server Error