Like what's been said. Transplant, like last month. I never remove the yellow leaves as the plant is eating them and removing them before they fall is like starving her further. That's one big plant. How about a picture of the whole plant. When I grow outdoors I try to have atleast a gallon of soil for every foot of height 2 gallons a foot if you're growing a wide tall plant. The soil is so depleted. The only way I can describe this, and bare with me here..if I ate supper, then, now bare with me here, have my after supper trip to the can. Now bare with me here, how many times could we eat said trip to the can and make another trip to the can before we completely deplete the nutrients and die.
Anyways make sure to atleast transplant before you flower or it might not give the best results.