How to flash to a customized size emmc (64GB) in TX1

I just replace the onboard emmc from 16gb to 64gb, when I try to use the SDKManager flash the board, only 16gb space is used, the left space is unallocated and in the last of the partitions. I tried modify the ROOTFS size to 54G in tx1.conf file, I could get a 14GB partition and a 40GB unallocated space next to it. but after I use resize2fs and reboot the device. It can’t boot.

Change emmc on SOM is not supported.

I already changed the emmc, and I can boot with only 14gb used. How to use the full space like using a HDD drive.