You can buy iFile like the poster said. IMO it's well worth the money as it's really simple and easy to use.
If you want a freebie, you can download either
iPhoneExplorer or
iFunBox. I think iFunBox is Windows only while iPhoneExlporer is either Win/Mac.
Both of these you'll simply need to install on your PC/Mac and then plug your phone in via the USB cable. Once plugged in, you'll be able to view the root files of your phone and navigate through them. It's just like using Windows Explorer except it's on your iPhone.
Once you get the hang of this, then you can follow the instructions on my previous post to find the folder/file you need to edit. As far as editing goes, you'll need to drag the Springboard.strings file onto your desktop in order to edit it. For Win you can use Text and if you're on a mac then you can use it's texteditor or TextWrangler if you like.
Once you've edited/saved your file, simply drag it back into the folder and overwrite the original file when prompted.
And, again, with iFile, you can do all this on your phone without the need to connect, drag, edit, reupload, etc. Much easier. I think it's $5 if you're interested.
As you're a newbie to this, I'd highly recommend you keep backups of whatever file you're changing just in case.