How to set upload_max_filesize in .htaccess?

php_value upload_max_filesize 30M is correct.

You will have to contact your hosters -- some don't allow you to change values in php.ini

If you are getting 500 - Internal server error that means you don't have permission to set these values by .htaccess. You have to contact your web server providers and ask to set AllowOverride Options for your host or to put these lines in their virtual host configuration file.

php_value memory_limit 30M
php_value post_max_size 100M
php_value upload_max_filesize 30M

Use all 3 in .htaccess after everything at last line. php_value post_max_size must be more than than the remaining two.