1) Download the latest firmware here and make sure you have at least 50% of battery left. Updating the firmware will also erase all the contents of the phone so make sure to back up all your data.
2) Extract these two files:
3) Open the SP Flash Tool folder and run the Flash_tool.exe
4) Once executed, click the Scatter Loading button and select the file as shown below.
5) After that click on the Download button. Just click yes on any prompt messages. Now connect your phone using the supplied USB and turn if off. Then, click on the power button briefly once. Do NOT hold the power button. Just press it for a short time.
6) A new device will be detected briefly (MediaTek Preloader USB VCOM Port). If it failed to install the driver, follow the steps numbered 1 to 7 (skip step 2) from this tutorial. There is also a bundled driver which came with the firmware so if everything else failed, try the bundled driver.
It should then start updating the firmware and shortly after you will have an updated firmware (dated 06/08). I do not really know the changes from the previous version so if anybody realised any differences before and after updating do comment below.
Disclaimer: I shall not be held responsible for anything bad which might result from following the steps above. This is exactly what I did to my phone and everything went well so hopefully yours should be fine too :).
PS: Here is the tutorial on how to root your ThL W3+ phone if you need it. Updating the firmware will unroot your phone.