It would be helpful if you mention the airline(s) you will fly to India and London.

Upgrades on international flights typically require redeeming miles issued by the airline operating the flight. This means you need a card which earns points that can be converted to miles in the appropriate airline flrequent flyer program, not "generic" miles that can be redeemed only for an award ticket. The upgrade rules vary more between carriers than do the rules for award tickets, but one class international roundtrip upgrades typically require 25,000 to 60,000 miles and may also require purchase of a specific fare class or a "co-payment".