How we can upright lingually tilted molars (36 & 46) while doing fix orthodontics. Cusps of upper molars touches buccal surface of lower molars.

Multiple methods. Your orthodontic specialist can discuss with you a variety of methods to "upright" lower molars and/or pull upper molars towards tongue (or simply tip them). This may include the use of "coordinated wires, " lower "expander or lingual arch, " elastics or rubber bands, etc., etc. In other words, it's not your job to sort out the biomechanics, that's your orthodontist's.
Wires & brackets. In %95 of my case I use wires and brackets to correct the problem you mention. One easy way is to add a bite block (ot not) and then add buccal crown torque to your wires in mandible. expansion in mn wire also leads to buccal tilting of the molars. there are more complicated solutions such as using TADs, buccal crossbite elastics (elastics from buccal in Mx to lingual in Mn molar). I like simple:)
Uprighting Molars. Uprighting of molars that are severly tipped "can be done" but could require temporary achorage devices (TADS) and or possibly intentional endodontic treatment of the uprighted molars. Only after a consult with an orthodontic specialist can you know what exactly will be entailed.
Treatment can work. The use of thick rectangular wires, a part of all orthodontic fixed appliance (braces) treatment, can normally provide the torque necessary to upright lingually displaced posterior teeth. In some instances, the use of elastics may be necessary to augment the uprighting forces. The doctor treating your case is in the best position to answer your question as it relates to your condition.
With alacrity. There are oh so many methods of tooth movement. A qualified orthodonticspecialist has an intellectual closet full of choices. And age is no barrier. Tooth movement can be accomplished at any age, it just takes a little longer for the "over the hill" crowd. Go see an orthodontist for an initial exam (usually complimentary) for an overview of your problem and a discussion of treatment choices.
TADs. Temporary anchorage devices (miniscrews) placed buccal to 36 and 46 with powerchains to the molars while supported with fixed appliances.
Mini-orthoimplant. Uprighting in the past required using the entire arch for anchorage. Today mini-implant is the best anchorage used in conjunction with spring to upright the molar. Schedule a consultation with an orthodontist using mini-orthoimplant. This method is very predictable in young patient (less than 21 years old). In older patient, root canal and crown fabrication is the best way.