How can I dismantle car alarm Ford Fiesta V reg?

Often my car alarm goes off when I lock the doors. If I leave the car unlocked the alarm does not go off. Also I am getting a warning light on the car when I am driving which states either a door or bonnet or boot is not closed properly so unsure if this is linked but I have checked all doors and seem ok. Can someone advise how to dismantle alarm, been quoted GBP 60 for someone to just come and look at it. Believe the alarm is factory fitted. Seen a few answers that state take the alarm fuse out is that safe and easy or is there any other options thanks.