How do I change brake pads on a bmw r1100rt year

This could be a case of stripping and cleanMy the calipers but in this case I would also be looking at the front master cylinder or an internal collapse in the brake lines. This second option is not unheard of in these bikes if they are still on the original rubber brake lines. Change them to braided lines regardless as at this age they will be well past their best.

Here's a very useful link for a video on how to do so: BMW R1100RT Brake lines replacement line bleed

BMW rotors are not known for lasting very much more than 30-45k miles. When the brakes are inspected, they measure the pads using a special tool threw the outer brake pad. Min spec is 3mm. When the pads are replaced, they measure the thickness of the rotors. The rotor spec is stamped on the rotor. if they are under that spec, they recommend replacing them as well. Next time you bring it in for service, just ask them to measure the rotor thinkness, (its not a huge task, all they have to do is take the wheels off). But more often than not, the rotors wear just as fast as the pads.

i have replaced both front/ rear pads, and no matter what the dash light will not go off. I have disconnected both front/rear sensors, and light is still on , any suggestions?

Brakes can vary in the amount of time that they last. For starters there are many diffrent grades of pads, the cheap pads last me about a month, but the good expensive pads last me 6-8months or so, and I drive really hard. So depending on how drive can determine how long they last. Usually you can replace your rear pads once for every two or three sets of front pads you replace as most of the braking work is done from the front. Pads are made intentionally to squeak when they are running down, so when you hear that squeak get em replaced, but if the rear's aren't squeaking just change the front and do the rears next time.

Good Luck
Hope this help