You need to use mod rewrite. There are ways to write them. You can also use a rewrite rule generator to understand how its done.
Below are the rules that needs to go into the .htaccess
file
# Rewrite --- example.com/your-new-key-is.php?key=5&submit=success => example.com/your-new-key-is-5/
RewriteCond %{QUERY_STRING} (^|&)key=5($|&)
RewriteCond %{QUERY_STRING} (^|&)submit=success($|&)
RewriteRule ^example\.com/your-new-key-is\.php$ /example.com/your-new-key-is-5/?&%{QUERY_STRING}
Here is a link to the Generator.
http://www.visiospark.com/mod-rewrite-rule-generator/
After you've written the rule to htaccess, you will enter in example.com/your-new-key-is-5/
which is equivalent to example.com/your-new-key-is.php?key=5&submit=success