One of the most common topics in the jailbreak forums is always theme editing and customization. To really be able to truly customize a theme, you need to know how to SSH into your iPhone. Anyone who is already familiar with web development and using an FTP client should be right at home. For the most part, FTP clients are also capable of SSH. If you don't have a client, don't worry, there's plenty of free ones.
And now for the typical disclaimer - if you aren't comfortable messing with your phone's file system and the possibility of having to completely restore if something goes wrong, don't proceed any further. As always, we aren't responsible for any damage you may do to your phone, so proceed at your own risk. If this all sounds okay to you, read on iPhone ninja!
1. Download an FTP client. In the video, I'm using CyberDuck, which is a Mac client for FTP. You can also use Fugu or iPhone Explorer. If you're a windows user, iPhone Explorer has a Windows version or you can use something like SmartFTP.
2. Install OpenSSH and SBSettings to your iPhone. Most of you probably already have SBSettings, but you'll need OpenSSH to be able to access your iPhone's file system.
And don't forget, at some point, change your iPhone's root and user passwords! If you need help with this, jump over to the Forums. OpenSSH and SBSettings can both be downloaded through Cydia or Rock, your preference. SBSettings isn't necessary, but it gives you a very easy way to toggle SSH on and off. Here's a ninja tip, whenever you aren't actively using SSH, turn it off. It not only further protects you from unauthorized access, but SSH is a huge battery hog. So when you're not using it, just switch it off.
3. Alright now that we've got that taken care of, you'll need to do one of the following after SSH is enabled on your iPhone:
Click the blue arrow, like in the image below, IP address is what you're looking for, write it down.
4. For FTP users, you'll need to enter your iPhone's IP address and make sure the port is set to 22. Your username is root and the default password is 'alpine' (without the quotes). Then click connect or continue. If you're successful, you should now have a list of all your iPhone's files. (Note: over wi-fi, you don't have to have your iPhone plugged in, but I'd recommend it so it doesn't kill your battery)
5. You'll now see a list of files you can navigate through, to get to your themes for editing, simply click Library ---> Themes and all the themes you've downloaded should be in there. Next jump down to the video for a walk-through of how to alter/change/add files in existing themes as well as create your own custom themes! And one more ninja tip, go into Settings --> Autolock --> Never. Sometimes when you're SSH'ing and your screen goes off, your SSH client will give you an error, so turn off auto-lock while you're customizing.