Get a hardware flasher is step one. The easiest for noobs is the e3. Once you get the hardware flasher, and a factory service mode device, then you can follow anyone of the tuts pertaining to the flasher you get.
The e3 is a hardware flasher, that offers a solder less solution. Other hardware flashers offer this as well, but it is a bit less complicated. If you get the needed equipment for downgraded as stated before, then people will help you downgrade. Without it there is nothing that can be done. Thanks
If you are lucky, you may be close to someone who provide downgrade service for a minimal fee. I think there are a few of them if you are in the US. They charge only a fraction of the cost compared to buying the devices needed to downgrade. I saw someone on eBay charging $50 and he has a pretty good rating there. I would have bought his service if he is in Canada. I am in the same boat as you, except that I am on 4.20 OFW. I'm still looking for someone who can help me out.