how can i manually change the time on my 7961 series phones

How do I go about reloading the IOS on a 3500 XL. The clearer and more thorough the better- im picking up the job of a lost employee!

does suscriber cm pull time from publisher? so if i manually update time on publisher, reboot both, both will have same time?

I want to specify an external mask for my lines... but when I do this on my own DN for example, on my 7940 display in the upper right, it displays my number as my external mask too. How can I have my phones' display only display my actual 4 digit DN,...

For my 7911G's, Im required to update phone firmware to "8.0(4)SR3 or 8.2(1)" for DST.When I view the webpage for my phone, I see "App load ID", "Boot load ID", "Version".....Well which exactly is the "phone firmware" ???