Even though Windows Phone 8.1 developer preview was released earlier last month, Huawei Ascend W1 were not able to update to the new OS because of firmware / driver issues. In fact, there was enough of a chance that it would brick phones for MS to stop its deployment till the problem could be fixed.
An XDA user has made a tutorial on how to get WP8.1 on the Huawei Ascend W1. All the steps are mentioned in this XDA thread. Basically you will need to install Qualcomm driver, followed by its I/O driver and support tool. After that you will be putting custom bootloader onboard to get WP8.1 up and running.
The developer was kind enough to make an easy-to-use video as well.