How can I fix my Veritas House Alarm?

Green light is flashing, I have tried to turn off 'alarm' switch in fuse box but alarm goes off. Also happens when I turn off 'main switch in fuse box. Similarly, when I try to take off front cover of other box the 'tamper' light comes on & alarm goes off.... Did notice that green light went off when power was cut. If I need a new battery/fuse, how do I replace without alarm going off??