It depends on kind of hosting that you have:
If you have SSH console, then you can do it on hosting after step 2, if you haven't then do it locally: run command
php app/console cache:clear --env=prod'.
Suppose you have on you hosting folders
youdomain/public_html, so in public_html must be located all web
files. So you must upload all from Symfony project (folders:
app, src, vendors, bin; files: deps, deps.lock), except for folder web
in folder youdomain. Everything from folder web upload to folder
public_html.
Check CHMOD for folders app/cache and app/logs, there
should be write access.
If there is no file .htaccess in public_html, then create it and add such code in it: https://raw.github.com/symfony/symfony-standard/master/web/.htaccess
Now you should use youdomain.com/index instead of
youdomain.com/app_dev.php/index, that you use locally. If a site still
did not works, you can open file web/config.php and find a code where
a check for IP performs, you find there only IP 127.0.0.1. Add your
current IP to this list and upload new config on the server. Then you
can open path yourdomain/config.php and check what's wrong. If
config.php shows that everything ok, but it still didn't work, you can
enable app_dev.php to debug: open app/app_dev.php and your IP the same way as in
config.php. Now you can run scripts as locally using app_dev.php.