If you fine with the bugs then you can try CM13 rom for redmi 1s by following below steps on How to install Cm 13 rom in Xiaomi redmi 1s.
1.Your device must be rooted
2.Any custom recovery is required (TWRP/CWM).
3.Make backup of current Rom before flashing Cm13 rom.
#How To Install CM13 Rom Xiaomi Redmi 1S
1.Download the Cm13 rom Redmi 1S and gapps for CM 13.
2.Then Copy it in your in your device in sd card.
3.Now reboot to Recovery mode and flash Android marshmallow rom in your device.
4.Then flash gapps file from reovery.
5.Now Clear cache and Clear Data.(Full Wipe Preferred)
6.Reboot your device.
Done! you just flash cyanogenmod 13 rom in your Xiaomi redmi 1s.Enjoy Android Marshmallow 6.0.