Checked to see if the second(smaller) return in hallway past kitchen. There is no usable access into the attic at this time, so I had to take the grill and can down to check. There is space to increase the size of the can length wise but not by width. We can get a 25x14 can and grill in. Upsizing the duct would be extremely difficult now. The attic is blown in with deep bury, so anything we do will make a good sized mess.