How to divide clock interrupt down?

Thank you mem, that code make lots more seance to me!

Do I just replace my existing 'void loop()' or do i need to remove void setup_timer2 too and add something to setup?

........as I get the error

 In function 'void loop()':
error: 'prevMillis' was not declared in this scop

when i just replace my existing 'void loop()'

THANK YOU ALL FOR YOUR HELP AND TIME! :-*