The Amiga 500, 1000 and 2000 are still extremely interesting computers because practically all of the chips on their motherboards are socketed. This means it's dead-easy to rip them out and replace them. Some chip upgrades simply replace one integrated circuit with a newer, shinier version. Other upgrades go full-monty on the chip socket and plug complete circuit boards onto the humble Amiga.
My first upgrade was a modest one. I bumped the Kickstart firmware from version 1.2 to 3.1 for a single reason: support for hard disks. My final goal with this upgrade path is to embed a single 4GB compact flash card inside the Amiga 500 case which will contain all my favorite games from yesteryear as well as a serious operating environment for some playful software hacking. The standard 1.x Kickstart doesn't cut it and the vintage A590, with its embedded controller circuitry, simply isn't as attractive as it used to be.
So what is Kickstart?
Kickstart is the ROM part of the Amiga's operating system. It contains the most basic software functions that make an Amiga into what it is. I have yet to look into the code of a Kickstart ROM, but for one it contains what one would nowadays call a cross between device drivers and BIOS routines for all manner of hardware.
Replacing the Kickstart ROM means actually ripping out an existing chip and replacing it with a new one. So no downloading and flashing a firmware from the internet like you may be used to from your new-fangled Android devices.
I had my Kickstart 3.1 ROM shipped to me from Germany. At the same time I ordered a bunch of 40-pin IC sockets, some wire and a soldering iron. On Amiga 500 revisions 6 and up this upgrade is a simple matter of plugging in the new chip and forgetting about it. My revision 5 model requires a bit of extra soldering.
Now it's been nearly 15 years since I last touched a soldering iron, so I decided to practice on the dirt-cheap empty sockets first. It's a good thing I did, because I ruined two of them before I finally got the hang of soldering small components again. By applying the soldering modifications to just a socket I managed avoid soldering wires onto the actual motherboard, plus it'd be easy to undo the upgrade if need be. Simply pull out the whole contraption and plug the original 1.2 chip back into the original socket.
Upgrading a rev 5 Amiga 500
The actual upgrade on a socket is essentially simple. Connect a wire between pins 1 and 31. Make sure you bend up pin 31 on the Kickstart chip itself, so it doesn't go into the socket. Push the chip's other pins down into the socket. Now solder another wire from pin 21 on the socket onto the bent-up pin 31 of the chip. The contraption may look a bit outlandish now, but it should be very easy to push it down into the motherboard's original socket.
Now, assuming you didn't short any of the pins, your Amiga 500 should boot up with a purple screen showing a floppy animation on the right and the rainbow-coloured Amiga logo on the left.