How do you exactly update this? You download the minor RC4 zip file or w/e, and simply replace the files using FTP. is that it or do you have to go to some link as well? ex: http./yoursite.com/something.php
Please see:
Upgrading SMF (http://docs.simplemachines.org/index.php?board=3.0;sort=subject)
Make sure you take a database backup before upgrading.
You're nearly there.
Once you have overwritten the files on your server, using the ones taken from the upgrade zip.
Type into your browser http://yoursitesname.com/upgrade.php and hit enter.
All being well, you will see the upgrade script, just run it following the prompts.
ysite did you manage to upgarde ok?
well i havent done it. Will it mess up my themes and mods? I really dont wana risk if any of that will change or is it possible to reset it back if anything goes wrong?
has long as you have a database backup nothing can really go wrong as you can revert that back and upload the new files then your mods etc. How do I backup my database? (http://docs.simplemachines.org/index.php?topic=492.0)
Keep in mind that you are using a release candidate so many of the files could have changed. The process for upgrading from RC3 to RC4 will pretty much be the same when 2.0 goes gold, in that you will need to replace files which will essentially remove your mods.
Making a backup before you start to upgrade should always be the number one thing to do. This gives you the option to return to that version if you need to.
I'd wait until v2 goes final, myself. ;)