Xiaomi has announced a beta version of their home-cooked ROM, MIUI 6, for the Redmi 1S.
The beta build is a work-in-progress, and will be updated every 1 or 2 weeks, and hence may have some bugs.
For example, here are two bugs present in the current build:
1. Phone occasionally has difficulty connecting to network after restarting
2. Phone battery occasionally drops quickly after rebooting
If that isn’t your cup of tea, you can wait for the stable build, which will be rolled out once every 4 to 6 weeks.
You can download the MIUI 6 beta for the Redmi 1S from this thread at the company’s MIUI Forums. Once you have downloaded the zip or tgz file, you will have to manually flash the update on your phone. You can find the instructions in another thread at the page linked above.
Screenshots of MIUI 6 for Redmi 1S: