We am using MCBSTM32C Keil Evaluation Board and MDK-ARM Realtime Library. This board accepts only SD Card of CLASS 2. Nowadays it is difficult to get CLASS 2 Memory card in the market. What are the software modifications (Code change) required to use Class 4 or any higher Class Memory Card.
I doubt it is a Class issue, the SDHC and SDXC cards have different commands/functionality, without support for those commands pretty much anything bigger than 2GB will not work.