After install TWRP recovery you can follow below guide on How to install Cm12.1 in Mi 4C.Do make sure to fulfill all the requirements given below before proceeding.
1.Your Xiaomi MI 4C Must be Rooted.
2.Must Have Custom Recovery in MI 4c like TWRP.
3.Make sure to Do backup of your current Rom from recovery.
4.Before flashing check for the bugs and stability report from here.
#How Install Cyanogenmod 12.1 in Xiaomi Mi 4C
1.Download Cyanogenmod 12.1 rom fro Mi 4c from the link given below in download section.
2.Download Google app for android lollipop 5.1.1 from the link given below.
3.Copy both the files into your device memory.
4.Now reboot your device into Recovery Mode that is TWRP recovery.
5.Now flash CM12.1 rom from TWRP recovery and then flash Gapps 5.1.1.
6.Do Clear Cache and Wipe Data.
7.Reboot Your device.Done! you have successfully flash Cm 12.1 rom in your mI 4c.