First question, can you close one eye and touch your index finger to your nose?
There are two options for upgrading to ER9x. You can solder 6 wires to soldering pads in various spots around the tx, or you can buy a board that touches these soldering pads. Both methods involve using a program to 'flash' the new firmware onto the ATMEGA chip.
I had a go at soldering. I'm not the world's best solderer, but it was really easy and is about 1/10 of the cost. I didn't leave anything behind in the tx, just unsoldered the wires after.
Why should you do it? It's just better. More functions, easier mixing, nicer to navigate and use.
Got it in one, Thurmond. If you can do that, you can easily solder the wires from an AVR programmer onto the soldering pads on the board. You just tin the tips of the wire, put a small amount of solder on the pads, then touch both together with the soldering iron momentarily and it's done.
You can get an 'AVR programmer' from Hobbyking or from ebay. Or you can get a Smartipants board (no solder solution) from Parkeflier or type it into Google.
For instructions on which wire to solder to which pad, BMSWEB has a good article on here, there's a wiki (type flash 9x with er9x into Google) or there are quite a few youtube videos. I found the hardest part was installing the driver for the programmer, which is a step regardless of whether you solder or not.
I left everything inside the radio. I soldered directly to the PCB and I modified the programmer so I have an USB port on the radio.
My mods also involved the FR-Sky module so I added another module to allow telemetry into ER9X.
LED and beeper mod and a indexed encoder to have precise PPM signals (for selecting Aeroplane flight modes)
My next big thing is the ERSKY board that replaces the PCB and adds tons of features.