First you decide what OS you want to install.
Then download it to your computer.
After you download the new OS to the PC you may want to delete any older ones you might have on it. You would only have one if you hooked your Storm up to the computer and ran the software that came with the phone.
I would do a back of of my device. This will backup your contacts, messages and device data. You will need to do a separate 3rd party app back up.
Then you can install the OS on your computer.
*If it is not an official release you will need to delete the Vendor.xml file. To do this you will need to find it. it is usually at the following address:
C:\Program Files\Common Files\Research in Motion\AppLoader\Vendor.xml*
Once you have backed up your device, installed the OS on your PC, and deleted the Vendor.xml file (if necessary) You are read to load the OS. To do so, you can either do it through the Desktop Manager or with the App Loader. I personally use the App Loader.
The App Loader is located in the AppLoader folder that the Vendor.xml file is located. It is a .exe with the berry looking device as the icon. Run that and follow the prompts on there and you should be good to go.
If you need me to clarify anything, don't hesitate to ask. Good Luck and welcome to again!
Your step by step was good. I just figured a few pictures might help also. My 1st OS upgrade was nerve racking. mfg: I would have felt more comfortable doing it had there been a few pictures to go along with the instructions.