When we have to upgrade a champion (any level), it would be much more time saving if we could select multiple max level champions that we wish to upgrade together and then select the required number of champions that we wish to sacrifice for the champion to increase it's rank. 

For instance, if I want to upgrade 10 grade 1 / rank 1 max  champions to rank 2, I should be able to select multiple of them together instead of hand picking one, then moving on to pick one champion to sacrifice. It takes a lot of time to complete the task if you have bunch champions to upgrade. Hope it makes sence :))