Download latest Android KitKat 4.4.2 stock firmware for Lenovo Sisley S90 smartphone from here or from here. Download previous firmware from here. Download another Lenovo firmware from here.
Model： Lenovo Sisley S90 smartphone
Image file size: 757 MB
Platform: Qualcomm Snapdragon 410 (MSM8916)
Caution: Please do not update firmware unless you know what you are doing, you really want it or it is absolutely necessary. Firmware updates may occasionally have bad results, like bricking your device, temporarily or permanently. The firmware update process is done entirely at your own risk. Before attempting to update the firmware, back up your data.