Replacing an old Wickes Burglar Alarm?

Hi, I want to replace a very poorly installed burglar alarm in a house i have bought and cannot find any instructions for uninstall. I know this sounds a bit dodgy but the wiring placement is terrible and just want to get rid and replace the system. The cable running to the sounder presumably will be tamper proofed and will sound if I simply cut it. The external sounder box I assume will also have some tamper switch. How do I remove it without not being able to silence it! It is a very old system with no identifying model number and Wickes just said it was obselete now and could not assist
Many thanks in advance for any help anyone can give me.