How to Reset the Computer in E320

I have a 2002 Mercedes Benz E320 that has now 8,870 original miles. I would like to know how to reset the message that states "Service A Exceeded by 70 days" . What is " Service A" message means. The automobile is mostly garaged and hardly driven.

Also I like to know how to chage the oil, I am somewhat mechinically inclined . How many quarts of oil it takes, is the oil drain plug easy access, is the oil filter easy access.

I'd love to know the same thing about the computer. Mine says service B, and i'm 12000 miles over it . A mechanic once told me over the phone it was the oil change, which of course I have had changed, but I'd love to stop this silly message.

press the menu button on the steering wheel until you see the mileage appear
next, press either arrow on the steering wheel until you see the serivce A or B message appear
then press and hold the knob(about 5 sec) on the instrument cluster untill a message appears asking to confirm reset
press and hold again until it says service interval reset, or something to that extent.