Wickes alarm with no manual?

Hi all.
Usual story: We've just moved home and have a Wickes alarm but no manual and cannot see model number.
I have the previous owners code and can set/unset it but do not know how to change it or put in service mode etc. so I don't feel secure at the mo.
I have a pic but cannot attach to this forum but it has black keypad at top right (like a phone ie 1 to 9 plus *#) and 8 leds to the left of pad in 2 rows (Mains,1,2,3 then Day,4,5,Tamper).
Please can anyone help?
Kind regards, Steve