What Relieves Severe Pain In The Knees?

I am 74 years I have been having severe pain on both knees. I was told that is due to arthritis. I am working as a volunteer worker in an international organization in Chennai. My work involves sitting 3 hours in the morning and again 3 hours inthe after noon in front of the computer. My work place is about one furlong from my house. and the walking ground is uneven.consulted doctors a few times . Iwas advised not sit on the floor and so on. what exercise can you suggest and what else could you prescribe. I am eritis inavitab le with aging