Board Thread:General Discussion/@comment-98.176.213.81-20160401204622/@comment-28108155-20160402072246

You can exchange R and above cards with Rare_Medals in the "Edit Menu" section of the Menu.

For the 75 cards limit, you can get "card limit +5" in the Shop section for 100 jewels, and "card limit +15"  at the last serction of the first campaign map (see Items page).