Apple released the GM, or golden master, of iOS 6 to developers last night. It's the same version everyone else will get come September 19th, and you don't need to be a developer to install it (unlike the betas). All you need is the file and iTunes 10.7 on your computer, so, why wait? Install it right now.
First things first, update your iTunes. Once you've done that, back up. And I mean it. Back up to iTunes (right-click on your iDevice in iTunes and select "Back Up Now"), and back up to iCloud, if you're using it.
Then, while that's going on, it's time to go, err, find, the iOS 6 GM that's applicable for your device. LifeHacker has a handy list of places to procure them from, so jump on over there and get downloading. Once you've got the file, you'll need to extract it. On a Mac it's just a standard DMG file so double click and you're there, but on a PC you'll need something like 7zip to extract it.
Next all you need to do is hook up your iPhone, iPod touch or iPad to iTunes. Once plugged in select your iDevice in iTunes, hold option (or Ctrl on a PC), and hit the "Check for Update" button. That'll bring up a dialogue box where you can locate your downloaded and extracted iOS 6 file -- you've scanned it for viruses already, right? -- and hit OK.
Now, just sit back and wait while iTunes does its thing. 10-15 minutes later you should have a freshly installed iOS 6 device, hopefully with all your apps and settings in tow. If not, just restore from those backups you made and you should be golden.