Lowering my Tour bike gearing to MTB gearing I am going on cycling tour on the Himalayas through Tibet, Bhutan, India, Nepal and Pakistan on my Araya FED touring bike. Now I am thinking in changing my gear, crank which is SR-SUNTOUR XCT 48-38-28T×170mm w/Guard and my Cassette is SHIMANO CS-HG31-8 11-30T 8 speed, to very low gearing 10 speed. Would Changing to Shimano XT M782 3x10 setup (22.32.40) with an 11.36 cassette, help overcoming for many hours everyday for 3-4 month cycling the Himalayas? I think I have to change derailleurs, chains and more.  

Pleas I need some advise from mountain climber cyclists ( I come from very flat country,Denmark) , what groupset would give me the best range and lowest gears for climbing? Thanks beforehand.
To change from 8 to 10 you will need an upgrade to 10 speed shifters and likely a new derailleur. Almost certainly it would be cheaper to sell the bike and buy another, I would recommend against spending that amount of money on that bike. 

The rear derailleur should be OK, the Altus have a capacity of 43 and max cog size of 34. The front is rated 48MAx, 20 Capacity.  

A 8 or 9 speed 22/32/42(e.g. Shimano M361) crankset would be ideal, but are not that common in better quality sets.  22/30 is a seriously low gear, you will be riding slow enough maintaining balance will be a problem. You can also get a 11/34 8 speed cluster, giving an even lower 22/34 at the expense of wider gear inch gap.