I have covered 2 processes in detail in this post. Scroll down and read as per your need.
1. Manual update to bridge firmware ver 2.22.40.53
2. Manual upgrade to Lollipop 5.0
Since there were bugs the Zenfone 5 bridge update Ver WW 2.22.40.53 was stopped but its needed for a smooth transition from kitkat to Lollipop.So I will Show you step by step to first update to Ver WW.2.22.40.53 manually then update to Lollipop.
There is also a new FOTA update available for 2.22.40.54 WW .If you get that then update it instead of manually updating to 2.22.40.53( but some people mentioned that there are problems updating manually from 2.22.40.54)... so I suggest that you manually update to.2.22.40.53 to smoothly update to Lollipop.
Note : If you are already on the bridge firmware then scroll down directly to the Lollipop firmware update steps.