You can allow UTF8 characters in page names, or extend the default to allow for uppercase letters through the configuration. You need to update two config settings to tell ProcessWire to allow UTF8 page names and whitelist the characters you want to use, as well as update your .htaccess file to route those URLs to ProcessWire. This blog post has a detailed tutorial.
I haven't tested this, but if you only want to allow uppercase letters (and no UTF8 characters), it should be enough to add the uppercase letters to $config->pageNameWhitelist. The default .htaccess routing rule already includes A-Z characters, and uppercase letters are ASCII anyway ...