Sadly, unless the alarm was well-installed (and every one I've seen to date has been the opposite, even for insurance-compatible installers), it's going to be a bit ugly.
There will likely be cuts in the link between the ignition and somewhere else, thankfully normally just the one cable leading from the steering column back, there will be a link to the door sensors, likely a link to something measuring car voltages, possibly cabling dragged into the doors themselves where the solenoids are (and, bad luck, cuts to those cables too). In all, it's a bit of a clusterf$&k.
In my Prelude I had to re-solder and seal all the wires since the install was so bad.
Find a wiring guide for the alarm if you can, I got lucky and it helped me immensely. That permitted me to label ALL the wires and made reassembly a joy.
Assuming you're going to gut this thing from the car, the best way is probably to disconnect your battery and:
1. Find where the main alarm module is, my guess would be up against the right hand side of the footwell, behind the dash. You might be able to get to it moderately easily, you might not, once again dependent on the installer.
2. Drag the module out so it's visible along with all the wiring, leave it hooked up. It's likely the alarm's in a little sealed/armoured box, you're going to need to find a way to open it.
3. if there are additional sensors (ultrasonic, glass break) or modules/controllers (electric window, etc.), find these by following the wires from the sensor or from the main alarm module, remove the additional modules.
4. if cables lead into the doors, leave them for now, that part's a little ugly and will take some time.
5. follow the wires from the siren to the alarm module, remove that outright.
6. Follow the wires from the alarm to the ignition, or from the ignition to the alarm, these will likely be the relays, you'll probably want the Honda wiring guide at this stage from the service manual so you can re-connect and heat-shrink these wires. If you're _lucky_ they'll have skipped the steps where they're supposed to cut out sections of the ignition wire to stop people hotwiring the car, if you're unlucky you'll either need some cable to replace it of a similar gauge, or a new loom for the ignition :/
7. If there are any wires from the alarm module simply crimped/spliced onto others, undo those and seal the split in the insulation (wrap electrical tape around it and then a small cable tie, or if you're feeling fancy, pull one end of the cable from whatever plug it's in by wiggling out the pin from the plug/socket, slide some heat-shrink over it and seal it up good and proper)
So, now you should have removed the siren, fixed the ignition loom, removed additional sensors, possibly removed power from the alarm module itself. This should leave you with additional cabling from the module for god-alone-knows-what (you're on your own there, sorry) and the doors.
If the doors have had cabling fed into them somewhere, you're going to have to pull the door cards (sorry). If you _don't_ fix this and they'd split the loom to catch and trigger central locking then central locking won't work any more
Pull the door card, pull the alarm installer's awful wiring, join up the old wires (they should be colour coded), find some way to fix the plastic sheeting on the door that's probably cracked/torn. Fix any rattles while you're in there
I _think_ that's it. It's been a few years since I'd had to deal with installers handywork, and I'm kinda glad my current EP3 has the Honda-provided alarm.
Don't forget to notify your insurance company, It will likely affect your premiums and if you don't tell them then you might fail a claim (assuming you ever need to make one)
